Context
My boyfriend and I drove about 11 hours away to his cousins' wedding (bf = best man). His entire family was there. I say hi to everyone (met them before), including Y. About 30 minutes of general hellos and mingling. I've met Y briefly in the past. We got to the name part, because she had to drive 9 hours to make it back in time for work.
His sisters and I wound up sharing a room (3 total). This house is beyond its maximum capacity...one or two people slept in the hallway. Y pulls me into there after the 30 minutes of mingling to ask me more about myself (unfortunately I don't remember all of the questions). She tells me she feels like an outsider in the family, because she wasn't adopted by them until she was 5 years old. I don't remember what I said verbatim...something along the lines of "I'm sorry to hear that....that must have been hard."
Her: Oh well. "Being adopted" problems.
Then asks me to go through her wardrobe with her to pick something for tomorrow. "What do you think: this or this? I want to make sure I still have an ass in it." Tries on both, I tell her which one shows off her curves better.
She asks me to tell her more about myself. I get the feeling she wants me to share something deeply personal, but I'm not comfortable doing that with new people (unless I feel a strong connection with them or the conversation somehow leads that way and I use "deeply personal" events as examples). Thought of something personal that I was comfortable sharing: I moved recently, had to quit school back in my old location (subject matter was just too tough) and then start a new major over here. I moved to turn a new leaf.
Her response "Oh wow...quit school?"
Me: Yeah
More mingling for 20 minutes, found out shower schedule. Because the morning was going to be insane, both of us volunteered to shower at night. I asked her if she wanted any time in particular, she said "No, you can go first".
More mingling again for 45 minutes. Then we all went to bed. Y and I went to the room first. She asks me "What do you and _bf_ fight about?" I'm a little taken aback, but try to answer as honestly as possible "We don't really...sometimes it's like we are about to get into a fight, but it turns into a big joke and we don't care about it anymore."
Her: Well that's weird.
Y: Can I borrow your lotion?
Me: yeah sure
Y: Can I keep it for tomorrow?
Me: Hmm...yeah you can do that.
Y: Well I might not be here tomorrow morning
Me: Hmm...maybe it's better to leave it if you're not going to be around
Y: But I really need it...I get dry skin.
Me: Huh. Hmm.. (I'm thinking about whether I need it, when is the last time I used it, blah blah)
Y: Why are you doing that! You're just being so wishy washy...ugh..just tell me what you want.
Me: What? I was thinking aloud. You don't want to hear my deepest, innermost thoughts? (I'm joking)
Y: This isn't even thinking aloud, it's just...wishy washy! Just tell me what you want.
Me: *thinks about about a minute more* Keep it.
Day of the wedding, bf puts my keys on the table and says "Meet us at the place at ___ time." I say okay, still caught up in preparations. I look for my keys about 30 minutes before it's time to go and can't find them. I look everyone for them. I tell people "I can't find my keys...I'm supposed to be driving people. Anyone know where they are?" No one knew.
I go upstairs and Y is getting ready. "Have you seen my keys? I can't find them anymore. Bf put them on ___ table and they're not there anymore."
Y: No I haven't seen them.
I start looking upstairs. 5 minutes later Y says "I'm running late...god we're gonna be 10 minutes late, because of me."
Me: So we arrive a few minutes late. Take your time. We get there when we get there. They usually plan for a buffer of 20ish minutes at these things.
Y: So you're telling me everything will be fine?
Me: Well...things tend to work out. Just do what you gotta do.
I'm still scrambling, looking for my keys 5 minutes before we have to leave. She asks me "what are you doing?"
Me: Still looking for those keys! I don't understand where they could have gone. Ugh, this is bad. Maybe we need to call a taxi.
Her: I thought you told me everything is going to be okay.
Me: Guess I'm a hypocrite. (I laughed, I was nervous, but I figured it was a playful shot at me)
Everyone I was driving was informed that was searching for my keys prior to this. After the last conversation, I went downstairs and said I could not find them anywhere. I'm really, really sorry and will pay for a cab for everyone.
Y wound up finding someone else's keys and took us in their car. On the way there, she calls up a friend on her phone and talks about what happened. "Yeah she couldn't find her keys anywhere...who knows what would have happened if I wasn't around. Can't believe she lost her keys....yeah I know who does that?"
We get to the venue and it's wedding time. They planned it so there was over 45 minutes buffer, so we're there with more than enough time to spare. After the wedding, they have a photo shoot. Me and another relative's boyfriend hang out, talking (photographer doesn't want us in there, makes sense). Part way through the photo shoot, more relatives join us (about a circle of 6 people now) and we're all talking. Few more minutes and another 3 people come along, including Y. We're standing, talking for about 10 minutes. Then Y steps directly in front of me and the circle closes. I didn't see a entry point to get back in. I sporadically talked to those who were next to me, but it's pretty hard when there's a circle in place and you're outside of it.
After the reception, everyone goes back "home". I tell everyone I can't find my keys. At least 10 people start combing through the entire house, looking for them with me. This transpires for at least 30 minutes and they tell me "I just don't see them..I'm so sorry. I'll keep looking though". I go upstairs to the room. Y asks me what is going on down there. I said I am looking for my keys. She goes "Whatever....it's not a big deal. Why do you need them so bad anyway?"
I said "I have to leave in one day...and I may need to transport people. I need to find these keys as soon as possible."
She rolled her eyes at me and said "Well it's not a big deal okay?" Her tone seemed direct and defensive.
I said "I'd rather find them sooner than later."
Y: Fine....I'll look for them.
Goes downstairs, comes back up with them immediately.
Y: Oh...there were on the counter in the kitchen behind a box...that's probably why nobody found them.
There were 10 people looking for it. One of the main places they looked was in the kitchen. By looking, I meant EVERYTHING was removed from the counters and all boxes were also searched (I did this as well).
I'm confused, but thank her for finding them and putting my mind at ease. She still seems to be in a bad mood. I run into bf 10 minutes later and tell him what happened.
Bf: .....She had the keys this whole time.
Me: Huh...that's interesting. Maybe.
Bf: I wouldn't put it past her. And now she doesn't want anyone to know it's her fault, especially because she talked to her friend about you while you were right there (and another relative was there too).
At this point, it was just awkward and nerve-wracking. These are the majority of the interactions that happened. There were other smaller ones where I felt hostility.
We wound up driving her home (she was a 3 hours away from our location and wouldn't involve going out of our way). We committed to this before "lotion" conversation happened. During the conversation, bf brings up Socionics. Y seems interested so we talk to her about Socionics for the rest of the way. Went well, no more hostility.
What I did about it
Pretty much nothing. I wound up weeping instead and feeling completely helpless. Clearly not constructive and something I'd like to avoid in the future.
TL;DR
Went to cousin's wedding with bf. Bf's sister Y reached out to me at first. It seemed pleasant. I was uncomfortable with the personal questions, but went along with it anyway. I had to transport Y and one other person to the wedding later that day. I lost the keys. I apologized to everyone. Y found us a ride. Y talked about how things could have gone poorly if she hadn't found us a ride. At the wedding venue, Y physically stands in front of me while I am talking to other relatives in a circle. Later on, Y finds the keys, but it seems more likely than not that Y is the person who took them in the first place (who knows intentionally or not, but I doubt it). We drive her home (3 hours with her in the car) and talk about Socionics. Everything goes well.