How do I handle my mother with dementia, who's been very emotional and verbally abusive to me?

My mother's dementia began 5 yrs ago but was only dx this year, bc she refused to see a doctor. She's still in denial. We were always close but she suddenly turned on me. She accused me of all the things she was doing, said I was a liar. I lost my only sibling, my brother to suicide 2 years ago. I live 550 miles away from her. She's in assisted living. Since my brother's death, she's left with no family to take care of her, so my sister inlaw went behind my back and made arrangements to put my mother in assisted living, then got her to sign a POA naming my sister inlaw to make all decisions for her, even financial. My mother hat repeatedly said she will never give my sister inlaw that kind of control, however she has. Look I've called and asked mother what she had for lunch or dinner within 30min to an hour after and she doesn't remember. She gets extremely confused and couldn't remember her address and phone # last year!
I and my daughter surprised mother before Mother's Day to bring her home with us for a visit. After we arrived, my sister inlaw showed up angry that we were there because she was taking my mother to an attorney to get her to sign a POA! Mother had no idea where she was going and had no knowledge of what she was going to sign. I explained what the POA meant and she was very upset. She kept saying she wanted me to take care of those important matters because I was her daughter. She adamantly expressed this to my sister inlaw.
We we got to my home, my daughters and I were very concerned that my sister inlaw was trying to take advantage of mother. I called an attorney and told him what had happened and he met with me and said I needed to file for guardianship to protect mother. You must notify any next of kin, she had a bro and niece, both who lived in the same state, both in bad health and neither able or willing to take care of mother. I had been trying for 2 years to persuade mother to come live with me or just look at facilities near me, which are much nicer, have more people and entertainment for her plus memory care. She refused to leave her hometown. I did file for guardianship while she was at my home, not knowing if I needed to keep her with me because I had seen that her condition had deteriorated. I did everything legally, she would have her chance to talk to a judge and he would determine her competency. Whether she remained with me or not, no one would have been able to take advantage of her. When her bro and niece were notified by court of my filing fir guardianship, they called her, upset her, but they weren't willing to help me. She insisted on going home immediately and we would need to make arrangements. She called several people, I know she talked to my sister inlaw in addition to her bro and niece. Someone was so mean and vindictive that they told my mother I had abducted her and was not going to let her go home! Before I could get into court she had my sister inlaw, if all people coming to get her. Legally I couldn't stop her and anyway, I didn't want her upset any more. The next thing I know, my sister inlaw is arranging an estate sale of everything left in my mother's home, all had been left to me, and my daughter's and I were to move this fall. I was never called or consulted about anything. I learned that my mother had signed a contract, I explained that she shouldn't be signing anything, then I was told it didn't matter bc my sister inlaw was handling everything and she had POA! I knew if other things that my sister inlaw had done, one was keeping my mothers house bc we put it in my brother's name to remove my mother's name from the deed, never suspecting my bro would commit suicide and die. My sister inlaw was aware that my bro and I agreed to sell the house to use the money to take care of mother and anything left we would split. After my bro died, my sister inlaw brought my mother the property taxes and insurance bill and told her that the bills were HERS and they were for HER HOUSE. So my mother has paid those bills all the time thinking that her house still belonged to her. I have cried and pleaded with mother trying to make her understand that it isn't her house. Mother keeps insisting that my sister inlaw has been good to her. I have even reported this to Elder Abuse in the state, they investigated and informed me that my mother said she knew everything she had signed and it was all her decisions. My mother refuses to admit there is anything wrong with her. Anyone but me can talk her into anything, she's very gullible now. I spent all my $ trying to get the guardianship and now I have no funds to hire an attorney. Anytime I try to discuss this with mother, im yelled at and called a liar. She's even called just to be mean to me, then hangs up on me. I have already had an emotional breakdown and have been hospitalized twice because I can't handle it anymore. Yet I miss her and am unable now to even talk to her bc of the abuse. She isn't aware of what she did.