If they are not caught in the act then you do not have proof they did it.
If they are not held to account then not only could they do it to your mum but other vulnerable people as well.
I know it isn't the same but many years ago whilst on holiday with my OH we stayed in a guest house.
I suspected that something was wrong as we had too many mirrors in our room (and they reflected every angle)
I said to my OH that I was uncomfortable and did not trust we were not being watched...
after many days I convinced my OH to remove the suspect mirror (we went out and bought a screwdriver) ... to his horror and for me just confirmation...... yes there was a giant hole in the wall with a curtain in between
I called the police who said ... if you cannot prove he (the B&B owner) is watching you... then we do not have a case as he could say it was already there and he had nothing to do with it .... so we did... we set a trap and caught him .. he was indeed prosecuted (it is a much longer and funnier story ...for another day
)
but the gist is ... you have to prove it .....
and think of the others who have been victim or are yet to be victim