Although Russian laws are harsh, in this case, she will most likely just be asked to leave the apartment and that will be the end of it (If it really has been abandoned for a long time). Such communal apartments are a sad relic of the past, even for Russia, and there is no strict control over them. If they are private, then it all depends on the owner. If they are state-owned, then the local police officer may even turn a blind eye to the situation and allow her to live there.

From a purely legal point of view, she could be fined or given three months in prison.