Aww Kirsty poor Gemma, she must be so sore down there. Try to give her as much nappy free time as possible. I know that it's hard in the cold weather. Canasten is great. I use it more than one time a day on Tehs bum when she had thrush. Maybe alternate between the medicated cream and the other, make sure you clean off each layer for each change. The only problem with canasten and other thrush creams is that they come of really easy so 1 wee and it's gone. IYKWIM. Not really long enough to work. Try not to use wet ones on her bum either, a soft warm flannel will be so much more soothing.
I hope that some of this helps.