Sister controlling finances is making power play with decisions for mom and her care. Any advice?

I have had mom with me for two years and in in-home hospice care for 1 year. We thought we would lose her in February and I planned my first trip in June (thinking it would be ok). She rallied and by end of March I thought my June trip would be a problem. I confirmed with my sister that handles the finances that she would come stay with her that week but by end of April when mom was still thriving the excuses started. By end of April she was claiming that because she had invested thousands of dollars redoing her garden and has 2 dogs she could not commit to more than a few days. (she has a husband and 18 year old son at home) Mom had a rapid decline the day before mothers day. I called to tell my sister she was being transferred to an in-care facility. She was unable to come that day because she and hubby were picking up a new dog (now making total dog count 3) less than an hour from us and 3 hours from their home. Mom was in hospital 5 days returning back with me on a Wednesday. Talking with sister about my trip the following Monday and only 3 weeks prior to my departure to confirm what days she would be here, I am informed she will not come because of garden and dogs at all. (both of which were after the commitment) Now she is playing games with me, mom and money. Telling me no I won't do anything and telling mom, yes I will absolutely be there for you. After asking the social worker to step in and mediate the family drama it was confirmed my sister would not honor the only week she has been asked to help in two years to stay with mom in my home. Now 2 weeks before the trip I am scrambling to find suitable care and she is again playing games with the money (all of which is moms) telling the social worker money was available to pay while I was away but now not providing financial information to respite care. Now I am asking for full control since I am solely responsible but not sure how to handle the legality of it all. Even though social worker confirmed sister's neglect, mom still believes she's there for her. I am in a lose lose situation because I care about mom and sister believes she has outlived her welcome and is nothing but a burden and just needs to go for everyone's sake. I love mom and still want her to thrive as long as she can but I still have a family, with 3 kids of my own and a husband. I need to take college tours and vacations with them. I have canceled 3 trips already because of no help. How do I preserve my sanity and mom and remove the toxic sister?