Not sure how she got them but there are a few things to do until you can get some pam.

Change your substrate to paper towels. This way you can see the mites on the paper towel.

Clean out the entire enclosure really well and boil/bake all of the cage items to kill anything on them.

Wipe the snake down with a paper towel to see if you can get any mites off her.

Hope this helps!