What a terrible person! I agree with PP that she needs documentation. It's not enough to have a cashed check, he could hold it and cash it after the due date and say she paid late. She needs a receipt showing payment received and signed and dated by him. I agree that taking pictures or even having a neutral party walk through the apartment is a good idea. If he is slandering her character, who knows what he will say about the condition of the place.
As for a new place and references, if Lorrie has previous landlords, have them listed on the reference page. If 3 landlords give a good report and this guy gives a totally opposite report, it may raise a red flag like it did for a prospective realtor.
Lorrie does not say how long her lease is or how far into a lease she is. Contacting the housing authority may also help with this toxic situation. She may be taken advantage of (think extortion), especially if the rent is way too high for comparable condos.
Can she negotiate a lower rent? Or is it past that point?