I think it would be better for your relationship to tell her that it's just not a good fit for you and give her two weeks notice. If she takes it personally, then that's her issue.

Or, I would continue and make sure you stop at 5 hours, no matter how much work is left. And let her know that this is how much you can get done in 5 hours, period. You won't "volunteer" your time because this is a business relationship. You are an employee not an investor.

Good luck,

seesaw