hi. the laying on the back thing is good. but its because YOU dominate the dog. lay her on her back and STARE at her til she turns away. do that from time to time. not when she is "bad" just sometimes, when you are petting her, or playing.... she has to learn that you are the "boss"/alpha.
karen's right you have to star over. she has to learn that YOU are the boss/alpha/parent and that she depends on you. can you go to your local library? check out dogs for dummies or puppies for dummies (its a really great book with a really silly title). it teaches you how to be the alpha with your pet. i used it. and love it.

look for ads at community centers for dog training classes, those tend to be less expensive. you can also rent videos at blockbuster and hollywood video. they arent great but can help. i work with adults with disabilities, and understand how money can be tight.

good luck and keep writing for more suggestions!