Power of attorney of parent with dementia. Any recommendations?

Hello my question is: I have POA over my mother who is in a nursing home with short-term memory dementia. Recently I signed court documents on behalf of my mother to allow my 52 year old sister to file paternity (blood) test against a man who may be her father. She has know about this since age 18. This is something my Mother avoided all the years. I agreed to sign for blood test only. The petition was signed and my Mom listed as petitioner. This was not suppose to be. My sister was to be the petitioner not my mother. I only signed to agree to blood test, not to have my mother as Petitioner in this case. What are my rights in this? My sister has only visited my Mom 4 times in 10 months, two of which to meet me over this case.