Dwarf hamster low on weight

[Sukizmama]

Ok I have a two year old dwarf snow white hybrid. I have moved her to slightly bigger cage. She is cleaning up herself better. The yellow spots have almost went away. She is still very thin looking. Very picky about her food. We live in Georgia in USA. We don't seem to have all the choices you have in UK. Can anyone lead me to better food choices. I've been buying hamster food from Walmart and I don't trust pet smart. Please help!
I also have two Syrian hamsters both have good weight and fur is shiney and smooth clear eyes and both are growing strong and healthy.Looking to buy bigger cages, I have seen this cage that has five levels,we found it at Amazon.com . I am also looking how to make bigger bin cages do you have any ideas. Thank You.