legal rent/family matter question ?

It sounds like your mother is still on the lease, along with you, and your sister is living there with your mother's permission and your mother is supporting her by paying her half of the rent. What bills is she supposed to pay that she is not paying? Who is paying those bills, you or your mother?

What would you do if your sister moved out and you had to pay the entire rent by yourself?

What does your lease say about pets? If it says no pets are allowed, and your sister gets a dog, you can both be evicted. Make sure to point that out to your mother and sister.

What does your lease say about who is allowed to live in the apartment? Does it say only you and your mother are allowed to live there, or that you have to get the landlord's permission before someone else moves in? If so, you could end up getting evicted for having your sister living there without permission.

If you are allowed to have pets and your sister has permission to live there, about the only thing you can do is move when your lease is up. You would probably be happier living somewhere else since it sounds like you don't get along with your sister anyway.

One thing you don't want to do is get evicted, since that can make it really difficult to find another rental.

If your name is on the lease, and your sister's name isn't, your wishes will take precedent. You signed the contract - Sis didn't. You have the legal upper hand. The cops won't get involved, this is a civil matter.

You could always find another place and move out - let Sis and her dog struggle to pay the rent. And then there's the landlord - does he/she allow animals to live on the property? It sounds like you have a fair bit of leverage here, both morally and legally.

look on the lease agreement for pets, most places don,t allow them.Plus she is living with you , you have to put up with her pup i,d throw a fit,