What to feed an old, underweight pet mouse?

Hi I have a female mouse who is quite old (approx. 2years) and although she is still in good health, over the last 2 months she has lost 6g in weight bringing her from 32g to 26g. I was wondering what I could feed her to help her put on some weight as she does seem to be a bit too skinny at the moment. I cannot give her to many seeds as she has a seed intolerance and develops hot spots, and bald patches because of them. I have been feeding her a moles mix which consists mainly of coked brown rice oats, oat bran and moles. If anyone has any suggestions of what I could feed her either as a new diet or additional treats please let me know. Many thanks