How should I deal with my nosey sister-in-law? Help?

I'm so upset right now, it's not even funny. My sil (sister-in-law) and I clash because she's very nosey and I'm not. She loves to mend in other people's affairs. Thing is, my brother loves her of course and always takes her side. My elderly mom is now in the hospital, after suffering a mild stroke. She wants to stay in her own house, even though she's scared of a relapse and of fainting again. She has high blood pressure and she's now on medication. She's been through tremendous stress, especially after having been my dad's caregiver for 2 years. Anyway, now my sil talked to her about her "options", one of which would be isted living, which my mom doesn't want. My sil then told me that my mom would eventually be "forced" to make a decision. Sorry, but I'm not forcing my mom to do anything; I love her too much for that. If I have to stay temporarily with her, I'll do it, until she gets stabilized. Thing is, even if she's in an isted living residence or even a nursing home, she couldn't get 24/7 supervision. I mean, nurses aren't by your side at all times. Am I being too sensitive or what? I'm going crazy here. Apart from that, I'm the only one taking care of both my parents; all my other siblings live in other parts of the country. Help, please? I'm starting to feel terrible.