Who's in the wrong here?

Which wouldn't have mattered since you were up to 12.30 anyway.

I do think she should have said sorry, but she probably didn't understand how inconvenienced you were. She probably thought you would go to sleep and just get up to let her in and then back to bed. That's what I would have done had either of my young adult kids gone out without a key.

She's 20, of course she wasn't going to be back at 11, though.

Couldn't you have left the door on the latch or a key hidden somewhere at that point?

Honestly I think its a bit more your fault, shes 20 absolutely no reason you would wait up for her, it seems like your not sleeping properly anyway due to burnout and you took out your frustration (in your tone) at her.

It seems she knew you were annoyed at her so she got very upset when you were again passive aggressive the next day.
I think maybe you think your hiding your attitude and feelings a bit better than you are, and shes probably quite sensitive to small shifts in people's demeanors....I think a call would be best, and sooner so as not to drag it out, your probably both very tired and emotionally drained

There are two adults in this story.

Edit.

The more we infantilise people, I think the more they act like children. The niece is not without fault and a bit of reflection will do them good.

You are the adult, act like it.

No way should you be hosting visitors when you've so much else going on. Just text her and move on, and try to arrange some respite care at nights.

I suspect it's a generational thing - fragility and entitlement. Everything needs to be centred on them / to be nice.

I don't think either of you were particularly wrong. 20 year old in a night or get carried away leading to selfish behaviour but also a 20 year old is not going to know how to deal with their auntie being in crisis. Give yourself and her a break and make the first move towards reconciliation

@Whyohwhy1974: She burst in to tears and fled upstairs. She came back downstairs and said she was leaving. I said fine, do what you want. More tears. 10 minutes later, she'd packed and gone, saying it wasn't what she wanted but was giving me space.

But reading your later comments, she was only going home to her parents as she was only staying with you for a couple of days.

You were not being unreasoable at all, but it sounds like her reaction, while childish, was not so OTT if she was only staying with you for a day or two anyway.

I think you both need a few days apart and then you as the older adult reach out to break the ice. You don't need to apologise because you did nothing wrong but you both need to move on. But for goodness sake get her a key cut for next time.

Good points.

Except the niece didn’t say they were planning to go out on the lash. For all OP knew, it may have been a bit of welcome company and a bit of support.

The niece also came home hours later than she said she would, despite knowing that OP was likely waiting up - as discussed. If she knew she was going to be late or there was a chance of it? Say so.

Being 20 doesn’t automatically make you inconsiderate enough not to tell your host why you really want to stay nor unable to tell the time or ask for a key.

I would wager the tears were a ploy to make the OP feel guilty for having the cheek to be even more tired partly because of niece’s behaviour.

They know the score. Just as OP has the right to say no, niece should have the grace not to foist herself on a struggling relative just because it is more convenient for their social life.

@Whyohwhy1974 I think you are under too much pressure to look at things clearly. You wouldn't have reacted so strongly towards your niece if you hadn't been under so much strain.

She can be cold twice if she wants. But if you do that, people might be upset and feel unwelcome and leave.

I don't know where you got the idea that the niece asked OP to stay up for her? I think OP has repeatedly accepted that she should have just given her a key. Also OP didn't say she told her it wasn't OK to stay out later than planned or that it would mean she was staying up. I really feel for the OP but it's not normal to be "deranged with fatigue" and to get 4 hours sleep then snap at a guest about it. I would also have left (having tried twice to make pleasant chat) and let her calm down.

You literally asked: “Should I just be upbeat and smiley and suck it up and not react to her keeping me up til 1.30am. Or is she out of line?”

No! You apparently sounded pissy with her but you haven’t actually expressed in a face to face conversation with her why you are upset with her. That’s why. Instead of being arsey with her via your tone why don’t you explain to her like you’ve explained to us exactly why you are upset?

You are an adult, she is an adult- why don’t you have an adult conversation with her express your honest feelings about what happened? This all sounds very juvenile- you being arsey and her flouncing out but neither of you have actually talked like grown ups

I don't think either of you is the AH exactly, but why on earth did you say you'd wait up for your 20 year old niece? I can get doing this for an older teen like 16/17, but your niece has been an adult for 2 whole years! Just give her a key and get to bed. I find it hard to call you an AH because you obviously weren't trying to make her miserable, but it's fine for a 20 year old to come in when she wants with her own key, it was your choice to design a situation where you had to stay up!

So basically she acted like an irresponsible 20y old.
You are deranged with exhaustion and close to a mental breakdown yet thought it would be a good time to host family and are now being pissy that things have gone wrong. A 20y old cannot comprehend nor are they responsible for your level of exhaustion so it was up to you to admit this wasnt a good time. You cant assume everything will go well because it has on previous visits.
Tbh youve both acted poorly, however id say you are both embarrassed and should just get over it.

You get along with your niece, but she doesn’t seem to understand the stress you’re under or do anything to alleviate any of it. Does she cook your breakfast dinner clear up do the washing if she doesn’t do any of that I won’t bother having herto stay. you’ve got too much on.

I mean sure, I probably haven't been that tired, but it's on OP then to say no, I don't want to have visitors right now. No, I don't want to get up early to go on an outing with you. No, I don't want to wait up for you. No, you can't come home that late. The whole issue is that OP keeps saying yes to everything and then gets pissed off when the niece does the things she has said she is fine with.

Why didn’t she take a key? Did she ask for one and you declined, or did she not ask? Expecting anyone to leave keys under mats etc. is just not on - it’s the first place burglars look.

I had endless trouble with a dd invariably forgetting to take a key - it’s maddening! She had to learn the hard way - coming home unexpectedly mid afternoon, expecting me to be in, desperate for a poo…..

Yeah unfortunately this. Passive aggressiveness always escalates things.

Oh how dare someone be cold twice!!! <huge sarcasm>

Come on. She was staying at the OP. She asked for a favour - the OP staying up.
She then went on her words TWICE. And somehow she shouldn’t have expected the OP to be annoyed?
I don’t know, in my world, she should have profusely apologised first and foremost. Not waltzed in smiling.

As for the morning after, again as a 20yo,nshe is an adult and should be able to cope with someone saying ‘No im not well. I’m tired’. ESPECIALLY as she knows and will have the witness of the caring responsibilities the OP has (because said caring happens her in her house…). Not bursting into tears and then avoiding the OP.

Does she have a job?

So do it

Agree with this but the OP says “deranged with exhaustion” which is surely rather OTT.
Perhaps the action of the niece was a last straw,