1) No, even IF she were allowed to apply the rent to the repair (see below), that was a one time thing--one she's applied enough rent to cover the repair, she has to pay rent again. So she can't stay there indefinitely.2) There are times when a tenant may "repair and deduct" like this, but in order to do so:a) the tenant has to give the landlord notice of the problem; andb) the tenant has to give the landlord some reasonable opportunity to fix the problemand only if the landlord fails to take action despite notice and opportunity, is the tenant entitled to make the repair and withhold the rent. Based on what you write, it is unlikely that she acted properly, so when you go to court, the court may disallow her self-help remedy and require her to pay that rent to you. Going forward, if she doesn't provide notice and opportunity, she should not be allowed to do this; and in any event, the problems would have to be provably real *and* also problems of a type that affect habitability. So a major leak that is causing flooding, mold, etc.--that is something that a tenant may fix under the right circumstances. A leaky faucet that is merely annoying--no.