School Mother Copying

Hi
Please, I need help dealing with this. One of the mum's at my son's school copies A lot of things I do with my son. I've only ever once sad where my son goes swimming, then 2 weeks later she has booked in at the same time. She found out my son does tennis and has booked her kids in same time/day (she has twins). My son is starting at a new school and now she has msg'd me saying she has an interview with the same school. Trouble is one of her son's is extremely destructive in class and is very obsessed with my son, to the point where it really aggravates me, a lot. And for this reason of possesivness I felt the need to change schools before my son got older and into high school.
My question is, do I see the principal of new school (private) or leave it be.
I'm feeling devastated.