[Sapporo Guy]

Over here we would call that invasion of privacy. Basically illegal.
I wonder if this is similar to opening snail mail?

Before blocking her from your home. It sounds like this child needs some counseling or on a simpler line of thought, a family get together.

This might be the chance since she has been caught red handed.

It is possible a good chance to find out why your neice doesn't trust you and everybody else. I'm sure that she sees things differently than the rest of you.