She may have Aspergers, which would mena she is very poor at picking up on the sort of hints that you've been using. Aspies just don't notice them. If that is the case, the best thing you can do is be very direct--Polly's suggestions would work.
Or another learning disability. You have very closely described my daughter, who needs the type of hand holding you describe or she can't continue to work on the project (or even a problem). It's like there's a wall that prevents them from moving forward. I think you need to make clear to her as nicely as possible, what is appropriate.