Wellness dog food.

I have a 2 year old female Westie dog. I am feeding her Wellness,
simple solutions, mixed with Core. I am thinking of trying Evo and
after reading about it I think it might have a few more choices than
Wellness. Bella has been happy eating Wellness and I have mixed
in small mount of the wet canned Wellness with the dry. The only
reason I am thinking about changing is Bella has had a problem
with low platelets and I am doing every thing possible to keep that
count up. Once she gets off the prednisolone that the Dr. has been
giving her I don`t want to see the Platelets go down. I joined this
site to find help from anybody out there that might be able to help
me with info on the immune system and how to keep it healthy.
I had never heard about a dog having low platelets before this
happened. This is my 3rd Westie so this is upsetting for me to
have this happen. Will appreciate any help, thanks, Shaun.