After the backstory, I am wondering why you even want to have any communication with sis. I would recommend the ”I can't hear you” technique. I used to use this when my mother wanted to repeat old criticisms I had no intention of discussing, but she had lots of good points so I was ready to cut her off. When she got going on the phone, I would not say anything in response and just hold the phone away from me until there was silence. Then I would pick up the phone and talk brightly about something, anything else. ”I cooked the best chicken for dinner”, or ” The dog did the cutest thing today.”
You will not be able to convince your sister, do I recommend absolute silence any time she mentions soon, then change subject. Do not even act like you heard any direct questions. This technique really works.