Flash cards. Our daughter did very well using flash cards. We used them repeatedly prior to tests and she often received A's.
I think vitamin therapy, in conjunction with ADD medication can be helpful. In addition to getting a good night's rest. Also, having a good attitude and being in a positive frame of mind. Some of these things are really "minor," but a person has to take whatever they can get sometimes.
Anything you can do to help your child avoid saying things like "I'm retarded," would be a step in the right direction. Do whatever you can to convince the study hall teacher to help. Ask for even 20 minutes of specialized instruction each period and that would go a long way. Perhaps meet with her every other week and call her on the other weeks. Set yourself up a schedule to remind this teacher so that she will remember to help your daughter. Give her at least an idea of what she should be doing. Example: "Can you help my daughter on Mon through Wed. on Math and then at the end of the week in English." Each time you see her or speak with her, give her a little direction. Be sure to send her cards and or little gifts. Don't go overboard, but acknowledge her efforts. Being a teacher can be a difficult job and they appreciate the kindness.
p.s.
I got a chuckle out of your post, 'cause it reminded me that I read in Prevention Mag. not too long ago about one of the Herbs that is suppose to help a person remember simply by sniffing it. Guess what? I forgot what herb it is! I think it is Rosemary! If I remember, I will post. I'm going back to school and was thinking of keeping some in my briefcase.