What's wrong with this picture

Live in an apartment building with another tenant below me. Now this has gone on for some time and I can't really prove her doing this, but, with the water lines running up between the kitchen an bathroom wall, with the bathroom one going between my floor and her drop ceiling, tell me how it is possible to get hot water in the kitchen but not the bathroom for the tub 85% of the time? I know there's a shut off above her ceiling as the landlord had to turn it off twice to fix a pipe. Water comes out but it never gets hot. And I can't really prove that she is doing it.

Obvious Adam, she's not going to admit doing it, especially since she has no reason to be touching it in the first place. And yes, I have talked to her in general on other occasions with mixed results.

USA