to be a bit annoyed now?

[Intonational]

had a bit of a showdown with housemate re her boyfriend practically living here, needless to say while it has semi-worked (he now stays 4 nights a week which is still a lot, but whatever), she has distanced herself a bit from the two of us who complained about it in the first place. We continue to make an effort with her, invite her to things, talk to her, include her in conversations, and her boyfriend too - but while they have meals and cook in communal areas, she only really replies to be polite and doesn't engage in anything other than necessary conversation. Fine. (We are living at the property for another six months at least and I don't think anyone wants to move out btw.)

WHen she had family/friends over in the past (ie before the discussion), we all strived to include them and do things with them. Now I have a close family member down and have invited her to eat with us - she has listed off a series of plans she has today and said sorry she cant make it but to have fun... I am not desperate to have her there but annoyed there is an atmosphere after all this unfolded a few weeks ago... We are all making an effort so why cant she ?! SHe also messaged us recently imploring everyone not to take her silence personally and blaming mental health/asking for a bit of understanding (which I totally get - I have been there myself), but how hard is it just to respond nicely to people's attempts to want to reconcile? Even just superficially?

I guess I feel like she is punishing us when she was in the wrong to begin with - and is magnanimously being the bigger person by withdrawing and making us feel guilty... I don't know! But it's tiring and unfair

If she has but the withdrawal from doing group things down to mental health you may be over thinking it. Depending on what her illness is it could take a lot of effort to respond to efforts to reconcile. Maybe keep offering but don't take it personally if she can't/won't make the same effort

She's hurt. She doesn't take criticism well/ in an adult fashiom. Or she's manipulative and bears a grudge. That has affected the dynamic.
Either way she has plans. Accept that and drop it. It is very unusual to include housemates in family visits. Not for everyone perhaps?

She doesn't take criticism well/ in an adult fashiom. Or she's manipulative and bears a grudge. That has affected the dynamic.

Think you've hit the nail on the head

I know it's unusual, but it's her way of doing things and I have always done it for her - annoyed she can't offer me the same kindness tbh

Maybe she simply doesn't want to have dinner with your relative? She was perfectly polite about it. I'm not sure why you think she should want to, or should do so even if she doesn't want to? You share a living space, you're not in a relationship.

it's not about the dinner thing though, it's everyday life.

and it's annoying when you have done the same thing to someone else's relative and they refuse to do it with yours - im not even bothered, it's just the double standards of it - she insisted on taking our other housemate's mum out for wine as a twosome when housemate was at work and her mum arrived. That is what she's like