Basically, I have 2 sisters, one of which is really nice to me and we get along well, while the other is always making snide, malicious comments and IMO seeking to put people down. In the past, after our arguments I would always try to go and 'make up with her' regardless of who might have been in the wrong, and then we would normally make up but literally a few days later she would make a comment to me and be rude again. She dropped out of uni last year as she felt overwhelmed and couldn't handle it (and very likely has undiagnosed autism). Since last year, she hasn't had an actual job, but has been working at one of our family friend's gardens (she does get paid, but it's very much bc we are family friends). Now, next weekend this family friend is throwing a 'leaving party' for my sister bc she is going to university again. I happen to be working at my job on this day, and made clear to my mum that, due to my sister's constant rudeness and unwillingness to be anything resembling nice, I am not prepared to cancel my shift to attend this 'leaving party' (which is basically just an end of summer barbecue that would be happening anyway). My mum is getting really affected by this and saying it's 'tragic' that no one in this family supports one another - however I have never felt supported by this sister in any way and wouldn't expect her to come to a leaving party for my work if I had one, and I know she wouldn't want to go anyway. If i didn't have a shift myself, I'd be happy to just suck it up and go (I also don't know anyone else going as the other invitees are not mutual to me), however it's more the principle of cancelling my actual shift to play happy families for my rude and vindictive sister's leaving party from her not-actually-real job. I don't know whether to just go to please my mum, however I don't know why my mum doesn't see this as a symptom, rather than a cause, of my broken relationship with my sister, and that going to the party wouldn't change a single thing. Frankly, why should i sacrifice around $80 for this farce? I know a lot of this depends on who is 'at fault' in the broken relationship between me and my sister, IMO it's 80% her fault, but there's no point me telling 'my side of the story' to people who don't know either of us, so you'll have to judge without knowing that...