I moved to PA and I couldn't move into my house until the 12th of the month cause the landlord wasn't done with it and she won't prorate the rent can she do that or is there a law for this?

Were you able to move your belongings in? Is there a lease?

Wasn't able to move anything in until the 12th and there is a lease

What is the effective date of the lease? It should not take effect until you could take possession.

Unless the lease specifies that you cannot move in until the 12th but you will pay the full months rent anyway, I would only pay the pro-rated portion. If they have a problem with that, let them sue you. I suspect the court will agree.

I would negotiate - unless you want to start your tenancy with very bad feelings and possibly an eviction.

What does the landlord say about rent paid/no occupancy?