What kind of spray did they give you?
Put the snake on paper towels or newspaper until the mites are gone.
You need to spray the enclosure with Prevent-A-Mite. You can get some here.
http://www.pro-products.com/
It's the only sure thing that gets rid of mites safely for reptiles and for good.
Chances are, because she is a baby, she will be a bit nippy. It will generally get better with age and a little handling. She could just be hungry too.