Poor Shay-Shay! It looks like she has some pretty significant skin problems. The black, crusty appearance of the skin on her belly is called lichenification - it's caused by chronic itching over a long period of time.
There are a number of things that could cause severe itching, hair loss, and scabs like this. Some common possibilities would include allergies, fleas, a bacterial or fungal skin infection, or skin mites (mange). Treatment will depend on what the underlying problem is, so it's important to get a diagnosis first in order to know how to help her. I would recommend taking her to the vet this week for an exam - he/she can do some simple skin tests to help diagnose the problem and get her started on appropriate medication to treat it.