Oh, she knows where she is. According to her letter, she's essentially a slave in her own home. Her father (whom she warns us not to trust) has kept her mother out of the camps but seems to resent it.

Miss Perks said that she didn't write before because she's worried her mother wouldn't leave, not because she's happy where she is but because she'd be afraid that Sally-Anne might suffer in reprisal. But one of her friends had the idea that I could somehow help her mother fake her death (presumably since I have experience at that, although she should remember that was the Ministry).

Hang on, though, hasn't Molly met Mrs Perks?