I have a tenant that has taken in two cats. This is in violation of her signed lease with a NO PET policy. I have told her two different times she must get rid of the cats. She has ignored me in this demand. I want to make her move out by giving her two weeks to move and then I've told her I will change the locks on the doors. Can I do this legally. I see it as protecting my property.

No. You can evict her, but you have to follow whatever your local process is for doing that. If you do what you plan, she can sue you for an illegal eviction, and then you will get to pay her being forced to move.

Froggy is exactly right. You can't just change the locks. You have to follow the eviction laws in your location.

If a tenant is doing something that violates the terms of the lease then many states allow you to give a 3 day written notice to cease or vacate. If they don't comply then you can file the lawsuit after the 3 days.

At the top of the Real Estate Law forum is a sticky post that contains links to the landlord/tenant laws for all of the states. You can check there for the notice requirements for your location.

Yes, you may end up renting from her after her law suit againts you, for locking her out of her rental unless you have officially evicted her.

Depending on the area, you have to give her notice, and take her to housing court to be evicted.