It's simple don't engage with your sister when she directs her speech to the subject that you don't wish to discuss. Change the subject, if she redirects back to what she was saying do it again, on the third time it happens end the conversation with I need to answer the door, and will talk to you again soon.
Pod. Don't engage her at all on this topic because she WILL.NOT.STOP. I know from experience recently with my own sister. I tried engaging a few years ago when she was going off the deep-end with her own amateur psycho-babble and JADEing, which didn't work. I tried telling her I wouldn't discuss the topics any longer (this happened on more than one occasion). Didn't work. I tried changing the subject. Kinda worked (changing the subject meant me replying like this, "La la la la la la la; Papa Smurf is my friend" because, at the time, she was flaming me on my FB wall when I made the "mistake" of posting that I was waiting at the pharmacy for a prescription). I found the only thing to work was to refuse to address, period, what she insisted on discussing. However, I know this also involves your daughter so I would focus on your relationship
with your daughter and, maybe, explain to her why you weren't engaging your sister (well, maybe not, but do tell your daughter the positive things? Not sure on this one).
My sister, after she also tried to get to me through DH (then DF), dropped out of our wedding because I refused to be engaged in her asinine behavior towards me (unbeknownst to her, that saved us about $300 and a lot of headache so she doesn't know she did us a favor). It did cause some uncomfortable discussions with DH because he felt terrible about not acknowledging my sister, but I had to strongly argue that acknowledging her would mean that she wouldn't stop so he ignored her e-mails also. Guess what? It worked, and she stopped harassing DH and me.
I know you want to continue your relationship
with this sister, but it sounds like it might cost you progress with your daughter.