My sister with POA signed Mom's house over to her and husband and they took out mortgage. Can I take lien on the house for my half?

A little more information, please, so we can provide specific responses.

What do you think is your half?

Where is your mother? In a facility? At home? Being cared for by your sister?

Is she competent to make her own decisions? Have you seen the Will and/or Trust to know who specifically are the names heirs/beneficiaries?

What documentation/evidence do you have to support your claim that you have a 1/2 interest in the house?

What was the mortgage for? Was it to provide cash for taking care of your mother?

Could you tell us a little more. Did your mother sell or give them the house? Is your mother competent? What is the mortgage money being used for? We need a lot more information before anyone can answer.