I dont think YWBU.
Ok, she is 17 etc etc etc, but sometimes everybody just needs to suck it up and do stuff they don't want to. It was extremely rude of her not to say goodbye properly, IMO, her parents should have ensured that she did, it's just good manners.
I'm sure your DS was probably quite pleased/proud to have a 17 year old there. She could have said something like, "I'm sorry I cannot stay till ....... whatever the anticipated duration was........, I am going to a close friend's party tonight as well."
And on leaving, I'd make blooming sure my DS would say thanks and enjoy the rest of your party.
Manners cost nothing and it wouldn't have killed her to be a bit more polite/considerate.
Yes, I can well remember being that age myself and no, it wouldn't have thrilled me either, but I would have been made to (if I hadn't been willing) and I'd have been told to be civil, friendly and polite. I was always taught, when leaving a friend's house, to find the mum and say, "Mrs.........., thank you for having me."
We were not snobby or posh by any means, just taught good manners and social conventions.
My DC are 3 and 5, but I insist on good manners, please and thank you etc etc I have marched DS's up to staff in a cafe/soft play centre several times and made them apologise for making a mess etc. Yes, I know children can be careless and clumsy, so can adults, and if I have spilled or dropped something, I'd try and clear it up and apologise.
BTW, I am not some authoritarian parent, I sometimes let my DC get away with various small dismeanours 'cos I'm too worn out to stop them but I would absolutely not compromise/back down on good manners. I've often been told when they are out somewhere with other people, how well-mannered they are.
Manners and social skills cost nothing!! And yes, I'm sure they will turn into bratty teenagers at some point, but I still won't put up with bad manners/lack of consideration/thought for others. The toughest sanctions will be imposed.