Was this addressed in the first hearing, when is the next hearing? Counter with, she can go buy kids stay with you to keep relationship with father, stay in same school, and family. You are willing for her to have extended vacation time when kids are off from school. If you think she will go now, you can file a restraining order for the kids to stay in same school and not be taken out of state until the final hearing.
Then in the final paperwork, do not sign unless it states she will not move out of current school district or some people have 30 miles. Even with sole custody, if you have visitation every other weekend, she would still need the courts permission to move and change the order. Is she asking to move now?
Do you have a lawyer? Tell them you want a sentence or two added that limits or ability to move. "mother will not move children more than 30 miles without fathers written consent or the courts consent". If you are living close then try the school district instead of the 30 miles. How can she negotiate visitation if she will be out of state? Do you have temp orders to see kids now?