although i do agree that their choices are limited... if they want to go they should be given a chance. if they don't like it they can come home, that right there i think makes the difference. if they know that they don't have to go if they don't like it then they can enjoy it for what it is more. my dd (yes, she is in high school) doesn't always like all the classes she has to take and we talk about it alot, does she want to continue? is it worth it to her to do it in this certain way? can she get what she wants differently? for her it works this way, going to public school. that being said, maybe putting it off for another year, seeing what you can put together at home might work. what is it your dd is missing? what does she want that maybe she isn't getting at home? more social time? then make that happen. more "class structure" (because some kids love that, whether it fits into our ideal of unschooling or not), then see if maybe your parks and recs has classes or the library or the zoo, or see if maybe some other parents what to start up a schooling co-op. check out some workbooks and see if she likes just doing some "book work" for a bit everyday.
with my dd i put it on her. she can be homeschooled at any time, we can find a different experience for her if this isn't working. i don't get caught up in the tests and grades, and because of that she is doing great. one days she was telling me about how she got a "C" on a physics test, it was a hard test and lots of the kids didn't do "A" work, but she was the only one whose parent wouldn't care. my biggest thing was that understood what she missed so that she could get the most out of the class (which she picked to take) and she did.
although i wouldn't let my 7 year old smoke crack or do a beer bong, i would let him try out school. as long as they know they can come home at any time, i am willing to give it a go. some kids just do well in school. not everyone has the love of learning beat out of them. some kids LOVE worksheets and that level of structure. i have three that may never go to school and three who seem to want to at least try it. that is the nutty thing about people, they are all different.
i haven't read the whole thread, just skimmed a little so maybe this was already touched on.