I use cream occasionally, with a mircrofleece liner, so it doesnt ruin the nappy.

As a treatment however, go down to your local health store and grab some calandula flower tea and a packet of camomile tea (from woolworths is fine) and make up a batch, one tea bag and some a tablespoon of calandula tea (its usually loose) in a small pot or a cup each... let it cool then add a bit of cool water (half half) and use this to clean dd bottom with each nappy change (i made fleece wipes so that i can wash and reuse each day).
Also make up another batch and add to her nightly bath until it clears.
I would also recommend some nappy free time each day - playing in the garden or do you have floorboards or lino so that accidents can be easily wipped up? we have several hours of nappy free time every day, i believe this helps too

I use this solution and we have only once had an incidence of nappy rash and that was when we were away camping and i didnt use it and she had no nappy free time...

HTH