Lynzy, I am so sorry Mia2 is having a problem. Prayers are going out for her.
My understanding is that basically, white blood cells are produced to fight off bacteria, infection, viruses, yeast or fungi, parasites, or as a reaction to stress, allergies, etc. This is explained in this basic page without TMI:
High White Cell Blood Counts in Dogs - VetInfo
There are many many things that can cause elevated white blood count, so try to relax while the vets sort it out. We will all pray that it is something minor and easily treatable rather than some of the scarier things you might be fearing.
Hugs to you and Mia2