Hi,
Knowing her character be grateful for her thoughtfulness. She is obviously a very left-brained person who is by the sounds of it very introverted as well.
It is very hard to end things for most of us and she probably waited to make sure that the move was in fact going to be 100%.
Given that she is a teacher her children are probably not in your care in the summer and I feel she has given ample notice.
I does put a bit of stress on you to fill your spots but look at it as a positive. It’s amazing for new prospective clients to see that the people leaving have stayed with you as long as they did. To me it’s a huge reflection on the amazing job you do and service you provided to her children.
Trust me some amazing little one is waiting in the wings to come to you.