As long as there is no court order, or custody established, she is at liberty to do so, although, why on earth would she do that to her children?
He sounds like he's trying to be involved as any good father would be. Is he pycho? Is there a physical threat issue? If not, the fact is, she may cause herself more harm than good.
If he chooses to file a for custody, which he can and may do, once it's filed, those children become "property of the state". I asked my lawyer if I could move out of state, and he point blank told me no. Because there was a custody battle on the table.
She needs to double check with a lawyer. Some have free consultations. She needs to talk with someone. My ex-sister in law did that to my brother. It is viscious and mean. No matter how much you dislike someone, you made a choice long ago and fathers are play an important role in the lives of childre.
(Unless there are circumstances surrounding that illicit a flee she's being unfair.)
At the very least, tell him! It's not like he won't find out. And she can be found. I assure you anyone can be found. I found my uncle who skipped out after selling all my grandparents possions and a home worth over $300k! He fled hoping no one would find him. My hubby found him in 30 minutes!
Anger does funny things to people. Did to me. She better hope he doesn't find her after she does move. You never know what people may do, especially if you mess with their children.
If she's concerned about it to that extent, she should definately pray on it.
Check with the courts also.
Because Child support is established, he may have to agree to her moving.
It's a toss up.