Okay, deep breaths and a cup of tea first, mama.
Now, let's step back and look at this from a little bit of distance.
Daughter is nearly 18. You and she have not gotten along for some time. Many mothers and teen daughters don't.
Let's just guesstimate that the problems are partly your fault, partly her fault and partly nobody's fault but just circumstances.
I'm sure there were plenty of positives in there too, even if neither of you can remember them at the moment.
The friends are also making mistakes here, in my opinion. They are supporting your daughter, which I'm sure you appreciate. I'm sure you know she could turn to someone much worse for support. However, they are also intruding where they have no business being and taking sides based on what is by definition incomplete information.
So, that's where we're at. Everybody involved is partly right and partly wrong, correct? (We won't even discuss the deadbeat dad, though of course he deserves a gigantic helping of blame for this whole situation).
Now, what to do?
I suggest letting her go, with love. Not much point fighting it when even the authorities are coming back with "Well, she IS nearly eighteen." Okay, solved for now?
I'd say do not hand control of the finances over to the family friends. They can demand all they want, they're not running the show. Instead, do what you said, transfer money to her account as appropriate. If the authorities tell you to hand it over, then and only then do you hand it over. Solved for now also?
I have an online friend who was just hit with something like this, though her daughter is younger, 14 or 15 and the father is in the picture. Mother and daughter got into an argument. Mom put her foot down and said something like, my house, my rules. You WILL clean your bedroom or you'll be spending the entire summer with your father. Obviously, Mother was at her breaking point and fed up with the sass. Instead of cleaning her room, Daughter called her father to come get her, then refused to return home. Instead of supporting his ex-wife and reigning in the child, Father ran straight to his attorney and filed for custody. It was granted.
A few months of ugliness went by but then there was a lovely turn of events. Now teenage girl regularly visits mother and stays over sometimes. The longstanding mother- teen daughter warfare is over and the two of them are practically besties. Mother has a cute new boyfriend and a puppy and seems happier than she's been in a long time.
I could actually see this ending well too, where the two of you get along better than you have in years. I would just let her go if she wants to go. And let her come home if she wants to come home. Be calm, polite and nice to all concerned. Refuse to argue or re-hash who did what to who.
And, I'd speak to your daughter directly, not to the friends. If "almost eighteen" is old enough that you aren't allowed to control her, then it's old enough for her to be dealt with directly. The friends are overstepping and need to be treated according to their rightful place, not the place they incorrectly presume to hold.
But I'd be sure not to fight with the friends or badmouth them, because then you're helping to set up a tug-of-war situation. The friends aren't important and remember, they don't know what they are talking about. It's quite likely they'll get enough of her teen-attitude soon, when the newness wears of and they are the ones it's directed at. (And then you are permitted to silently howl with laughter haha). In the meantime, consider your new freedom. Enjoy your new freedom. It's all going to be okay. Best wishes.