Hello and welcome! I would also go with a Syrian - they're easier to handle for a six year old
We got our last Syrian when stepson was 6 and he still needed supervising as if our hammy moved he used to try and hold on to him a bit tight, but they soon learn how to handle them gently when shown. The hard bit was the two months it took us to tame ours! In the bathtub as little boy just wanted to hold him and he was wild! But we got there.
You could get a winter white as well maybe as it would be nice for her two see two different ones, but for handling I think I Syrian is best for a child. Some are quite hand tame from the start - ours was a nervous wreck, but so tame eventually.
As SKB says, anything sold as a winter white will be a hybrid, unless from a breeder with a pedigree - and they are prone to diabetes so a sugar free diet would be needed.
Looking forward to meeting your new hammy/hammies!