How to remove the name and details of driving liscence from their system?
She can ask, but they can decline. It's all part of scaring her into not stealing again.
There's no real need to worry about it.
It can help to understand that private security people have no special powers. They operate by fear and intimidation.
That's all this is.
It'll just be some private database that the security contractor keeps. It's nothing.
How can police access this system?
They can't browse it without consent, but they can ask for access if it's ever needed. And they won't.
Bottom line - tell her two things:
One, not to worry. As long as she doesn't steal again, this is over.
Her visa is not at risk over this. Border Force will not be coming through her door at 4am.
Two - that she needs to get (maybe medical) help for why she is stealing, and to help her not do it again.