I believe to some degree, kids go through this, my son has hygiene issues I'm working on. He'll be in the shower for 15-20 min, but not use soap or shampoo. I told him "Just so you know, don’t be surprised if someone says something about how you smell if you don’t shower properly, I love you no mater how bad you smell, but you are hitting puberty and smell like a man now" ( I don’t label him as stinky, I just say everyone is stinky, although I have said 'you can be known as the stinky kid if you want to, I'll still love you' ) Sometimes is important to him, other times it is not, well its always important to him, I just think he thinks he is fine with the efforts he puts into his hygiene, like a rinse is enough for today.
One thing that went through my head is I wonder if I took him to his Dr. and had his Dr. say something. Kind of like a medical instruction "you have to use a certain soap, dandruff shampoo, deodorant (etc) daily". Sometimes hearing it from someone else has an effect, Or, I've even thought "I keep hoping one of his friends says something and embarrasses him" not that I want him to suffer embarrassment, but I'm sure they smell him anyway, (then I realized when he had his friends over, they all stink)
It seams like it’s improved since he's starting to like girls, but maybe its just over whelming for some kids to turn into adults, sometimes I wished I didn’t have to shower every day. It's a lot to take care of our bodies; maybe she's just overwhelmed with all the responsibilities of it. Maybe having her start somewhere small and grow into the juggle of hygiene care will help her.
I hope she's not suffering psychological issues, she sounds pretty well adjusted other than her hygiene, maybe there could still be an issue and its showing through that one area, I don’t know. Maybe that is something worth talking to her Dr. about.
Sorry I have no answers, I'm just pondering with you.
Oh, another thing I have told my son is things like "who ever smells clean can ride in the car with me" or "I'll be happy to snuggle with you when you smell sweet" I love him and never want to criticize him to make the situation better, but sometimes even I have to draw a boundary and let him know that even thought I'll love him no matter how bad he smells, I still don’t have to sit and smell it.
Well good luck, let us know if you find something that works. I'd like to know too.