Have the school actually told her that if she moves out of catchment area her child has to change schools? Seems strange to me.
No. She is concerned as she is moving home soon. She had to fill in a form with all details of address etc before christmas as places were going to be allocated to children for the next step up in the school in september (From Nursery to Reception).
Details given were of the where she is living at present. She didn't know at the time of filling in the form that she would be moving outside of the catchment area.