8 weeks is very young for a chi pup to be away from its mommy! Yes, you can use a file since the nails are so small and soft. A metal emery board is going to be best, but if the cardboard type are what you have, it will probably get the job done at this age. Get her used to it now. Chi's are well known for not liking nail trims..lol So the more you do it, and the more you teach her what is acceptable behavior and what is not, the better off you will be in the years to come.
