Without checking back. Do you and she jointly own the house? If so, she may have a legal right of access.

If you want this to be the case, maybe you could ask her to pre-arrange with you when she comes, at a time you can be there.

As for changing locks. I'm not sure. Maybe others have views and will chime in...

T 13 M 7
Me 48 H 46
SS 15
BD 7.14 PA
D final 5.16 (H filed)

We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus