Dear M.,
Of course, I don't know what is going on, but there are strong symptoms of lack of security and need for closeness. Where is Dad? Maybe she would like to see him? What about an afterschool day care. A small church one where she can be with peers. You are doing the right thing about sitting with her while she does her homework - it is a great communication time, and don't listen to people who tell you that you are spending too much time with her. I could say mean words about that, for sure.
A clue for the future: Do listen to people, but do not act on their advice until you are convinced that it is the right thing for your family. Ask around, just like you are doing now, and the solution will come to you. No one knows the family needs better than mom or dad.
Good Luck, and keep trying until you find the answer, maybe you could ask her what is bothering her? Keep listening to her and she will eventually tell you, you have to make her feel very secure with you and that you will not get very mad about it. again, Good Luck, C. N.