Conservatorship; why is this mess now going through the court?

My sister put my Mother in a NH, 2 days after having her sign all new estate planning documents. I filed for Conservatorship and now the sis is opposing me. Our Mother has had her estate planning docs in order since 2001. She has always appointed me succ trustee, POA, etc., in fact, in the Trust doc and the POA it states should she ever need a Conservator, she appoints me. Now the whole thing is in Court, will probably go to trial. The sis will not tell or show anyone what the 2/17 Trust says, but am pretty sure she made herself sole beneficiary. Our mother has dementia, so the docs she had our mom sign are probably invalid. My question is: since I have been appointed succ trustee (and Conservator, should the need arise), why is this mess now going thru the court? By the way, the sister put her in a NH 2 days after signing the new Trust, etc. Then 2 days later, this sister went to mom’s home and stole all of her belongings, including her safe which contained her 2+ carat wedding ring. Mother has asked for her property back, the sis won’t give it. The Sheriffs say it is a civil matter. Prior to that, in the last couple of years this sis was taking our Mother around (3 counties) in her attempt to have mom sign new docs. Just before that, she was trying to persuade Mother to take all of her assets out of the trust, and naming the sis as sole beneficiary. She also tried to sell my Mothers house twice! She is in a NH now, but I would like her to be able to go back to her old house, with 24/hour caregivers. My Mother wants this very much. She is depressed and sad. Now it is in the courts, but, I wonder why, when Mother always wanted me to be her guardian, if she ever needed one, and she does. I dislike this sis so much, since 2012, when our Dad passed, and she handled the probate (he died w/o a will, she was not his POA...when I offered to do his final tax return she cussed me out and told me to speak to her lawyer. Then she says “Here, “B”, this is for you to remember dad by, and she gave me a pair of his sweatpants. She withdrew all cash from his accounts, even applied for and received 8 credit cards in his name (he knew nothing about it, he was in 4th stage cancer). I know when a person passes w/o a will, all children (parents were divorced like ago) are to receive notification re the probate. But that didn’t happen. I am still trying to find out how she was able to pull that one off. Also, I knew that once dad was gone she would go after Mother's assets, and bingo. We have a hearing tomorrow, I am going to ask why I am not Conservator, as she put that in over 12 documents, thru out the years, even a hand written one in 2016. I have an attorney, and when I write to him to ask these questions, he just sort of skirts around it. Don’t tell me to get another Attny, already have approximately $40 to $45,000 in him. I look forward to your help....