Rlyss

I'd say there's your answer. No offence to you mate but whatever you're doing down there with your hands probably doesn't feel sexual or sensuous or pleasurable to her. If she's only gradually refused to let you do anything with your hands then it sounds to me like you're groping her or otherwise doing something that isn't pleasurable.

If all she says is that she doesn't like it then you've got to find a balance between convincing her to tell you the truth, and not pressuring her to say anything she really doesn't want to say. I really can't think of any solutions except to ask her to be honest. She probably just doesn't want to hurt your feelings by saying that it feels like you're groping her, and instead blames it on herself or says she doesn't know why.