Her attitude is very negative and bitter about taking care of Mom and yet she refuses to let us step in and bring Mom to live with us. She has put herself on Mom's checking account and complains she needs more money to care for Mom. Mom told me that she is afraid of her. How do I go about getting Mom out of there without tipping my hand? I am afraid she will lash out at Mom if she figures out what I am about to do. I would like to administer a sound gourd thumping to her for terrorizing our mother.
Have you witnessed a lot of mistreatment? I ask this because sometimes elders complain about how wicked caregivers are, even when the caregiver has wings and a halo. It can have more to do with elder's feelings of loss and helplessness that are often turned on the caregiver. If you have witnessed abuse, by all means get your mother out of there. If it is just things you are hearing, spend more time and watch what is happening.
Are things bad between you and your sister? If they are good, maybe you could spend more time there and work out what you are going to do in the best interest of everyone involved.