That sounds super difficult. I lived in a home with only my mum and me in it and it must have been horrible for her. I wasn't as difficult as your DD but aged 17 she'd tell me to be home by 1pm and I would pay no notice, had no regard for her worrying while I stayed out till whenever I liked. As an adult I had a great relationship with her though.
If it makes you feel any better your friends teens probably aren't as nice as they seem. My 16YO has a friend who is lovely - everybody loves him - he's so nice, but I was shocked to hear him on the phone to his mum -grumpy is an understatement. Your friends teens might yet go through a difficult stage.
I know what it's like to feel you're the only one though. Although not difficult, my teens are very stubborn and don't ever listen to advice - even from other adults who they like and respect. Meanwhile most of their friends are studying hard and not almost getting permanently excluded from school for persistent lateness like she almost did. She's now doing a degree that was very difficult to get on to ( entry by audition) which sounds marvellous, except that her teacher and I didn't think she would like it and now in her second year she doesn't like it and isn't happy but is determined to stick it out for another two years. I worry about it often. She moved into a flat I didn't think she'd like despite my advice. Surprise surprise there are problems with it as I predicted. I worry that she will never be happy.....
But she did become instantly grateful for meals, lifts etc as soon as she left home. I'm sure your DD will come out of this phase too. I suppose my DD is making progress in that she does now at least admit that she hasn't made the best choices always.
However I know that's small stuff compared to your DD. I do have some advice;
Don't comment on boyfriends ever - however difficult - (DD had a bf who wasn't nice when she was 15). Be welcoming to him but don't give her advice. Be there for her with tlc when it ends. Which it will. She'll be enjoying the drama of knowing that you don't approve, so try to give the impression that you've changed your mind and realise that as she's about to turn 15 you won't advise her unless she asks.
Compliment her for anything you can think of whenever possible - anything - sense of fun/style/love of carrots/anything. Make her feel loved just for being her.
Acknowledge that it must be hard for her living in a home with only one other person. Encourage her to talk about stuff with another adult? Aunt, GP, family friend.
Do something regularly for yourself.
Don't blame yourself.
Don't accept swearing - tell her quietly that you're not listening if she starts and walk away. As calmly as possible. Try not to seem bothered by her language - don't add to the drama - but be matter-of-fact, briskly not accepting.
Try not to let her know that you are worried and stressed if possible.
I hope this doesn't sound patronising - apologies if some of this is irrelevant.