Read through the OP and I know I'm beating a dead horse here but I also feel like the OP is a) unnecessarily beating herself up over something that probably wasn't her fault per-se and I also feel like her daughter's situation isn't really *that* bad. (Tip: she didn't read too many Jane Austin novels. She's nineteen.)
My own story -- I was forced into an involuntary caregiver role around sixteen after my mom started to become very sick. I also helped financially support our family and was working about 60 hours a week on top of honors classes in highschool while helping to care for my ailing mom. When I turned eighteen, I got the heck out of dodge. I received a very generous in-state scholarship which I declined to get as far away as possible -- I moved to North Dakota, shacked up with my now-husband of six years (then long-distance/quasi-internet boyfriend) and took up schooling there.
My younger sister took up my role, but she stayed around after she barely graduated from highschool. Ended up with a guy that no one in our family approved of at that time -- community college drop-out, with aspirations to be "in a band" or the owner of a headshop(!!!). They've gone through some hard times as a couple but are still together after almost six years and he's grown to gain our acceptance into the family because he's grown into a decent guy and, as my mother finally was able to accept while she was dying, "he makes her happy."
Y'know what? We're both okay. It really is okay to make questionable choices when you're young. Several posters mentioned how easy it is to blur the lines of the parent/child relationship when the boundaries are not solidly typical. It's something that I never thought about until it was brought up here but completely explains the relationship that I had with my own mom.
Space and time are needed on both ends. Seems as if the OP really needs a therapist too -- she seems to have a lot of anger directed towards her daughter, which might be justified in many ways, but I bet your daughter can feel that anger.