Does the mother have any grounds to keep my daughter in the same school district?

I am the legal custodial parent. I have been for the past 8 years. Recently, we went to court and I agreed to let my daughter stay in the same school district because we moved. Now, the district she was in is severely overpopulated and not accepting inter transfers. Being she will be going to junior high, we want to just have her go to school closer to home. Her mother who recently moved to the same school district whom has visitation only has gotten an attorney demanding I use her address to keep my daughter in the same school district. My daughter lives with me and my address is her address.