The girl is still 19 and, though legally adult and over the age of consent, she's still OP's DD and you don't magically turn off all concern for them just because they've passed certain birthdays.
If OP saw bruises, would you be saying butt out? If 'no' then do you rate potential psychological abuse as serious? For OP described a change in her DD's personality and behaviour. If you thought that might be drugs causing the changes rather than domestic abuse, would it still be 'butt out'?
OP, if you are worried about her, then I think you should act on it. At university, teens get a first chance at living away from home and can make mistakes. You've ascribed the changes to the unpleasant BF, but do you actually know this for sure? I think you need to find ways to reinforce communication between you and DD (if she's away some of thtime, it's quite likel it needs attention). And then, without mention the BF, talk about how she seems a but different, ask what's up and listen to what she says.
I take it no younger siblings? Because they would be the bet at pointing out effectively that she stinks. Never say anything about the BF smell, just open windows and buy reed diffusers (or whatever). Don't say why, just let her notice (maybe) and in the unlikely event she asks, be vague "I thought there was a really nasty smell, I can't work out what it is or why it's lingering. Maybe it's got into the fabric. I hope it'll fade"
Can you invite other people round when the BF visits? Maybe her school friends or those from clubs/activities? Again, never say anything about him. Just provide the opportunity for herto make her own comparisons between peer groups.
That's assuming that there is no disclosure from her about psychological abuse or drugs. If those occur, then you'd need to seek specialist advice ASAP.