My son used to do the same thing. I tried everything - and I mean EVERYTHING. In the end (after a while mind you) I realised he was only itching where his singlet was touching his skin. So I stopped putting singlets on him and used tshirt material body suits instead which solved the problem. He's now 11 and still gets eczema if he wears a singlet. SO maybe try her without a singlet for a bit and see if it helps any.

Put some Sigma ZSC powder (i think it's Sigma, in a white bottle with blue label you get it from the Chemist) on her neck and body. Maybe also try some anti fungal cream on her neck, the dribbling on it could cause a fungal thing. Just a thought.