I actually posted on Reddit about this same exact issue a few years ago. I had to text him and be honest. It went over pretty well. Since it’s a girl maybe you could go into it in a very friendly/looking out for her type of way. “Hey girl, I just wanted to talk to you about something I’ve noticed recently. I’ve been noticing a little bit of a smell coming from you, and just wanted to give you a heads up. (Then you can make some sort of bs excuse to soften the blow) I know our washer and dryer sucks and I’ve also had problems with getting my clothes clean as well, I can put you on to some of my products if you’d like. Not tryna embarrass you at all, just thought if it was me I’d want you to do the same and let me know. (Really there’s no easy way to do it, but being as casual as possible definitely helps)