Can property management make me pay $1600 pet deposits just all of a sudden, no pre-move in inspection?

Ok, so my mom used to own her home. My parents divorced and she got the house. My mom couldn't afford the mortgage so she (idiotically) gave my dad the house and now she pays him rent (even after she payed $75,000 of her alimony into the house). She has had pets for many years (had them while she owned the home). Anyhow the property management company recently did an inspection and said she now owes them $1600 in pet deposits. Um, what the heck? The pets have done no damage whatsoever. There was no pre- movein inspection or anything to even be able to tell if the pets caused damage. Is this ethical for them to charge? Can she fight this? I think it's ridiculous because the pets have always been there and now all of a sudden the property management is trying to charge her randomly. I think my dad is trying to make my mom's life hell just because he can, the divorce was very ugly.
Added (1). The current lease has no mention of pets, or anything saying if she has pets they'll charge her $1600 in pet deposits. The bad thing is she is on a month to month lease, I believe.

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