Hey Wbee, I forgot to mention before ...
I'm so sorry things are hard with your sister right now. I think the big dark secret of struggling with TTC is how hard it can be on relationships. At first I thought I was the only one to have this problem, but since then I have heard over and over how it strains people's relationships with friends, family, co-workers, etc.
I actually lost one of my closest oldest friends. Long story short, I thought I was having a miscarriage (back before diagnosed with huge fibroid), I called her for support (she had conceived her DD with IVF), and she wasn't very comforting and rushed off the phone. A week or two later when she called me to chat, I calmly told her I would soon get over it, but at the moment I was mad at her.
She told me she hadn't thought I was pregnant and didn't want to go along with my self-delusion. I conceded that she could be right, but if I was having the experience of a miscarriage whether it was real or not, I needed a friend in that moment. She said she was there for me and had not blown me off at all. We fought on the phone a few times (this was at the time a long-distance friendship). It got heated and she broke up with me because she didn't feel "seen or safe" (she's a therapist). I later tried to make things better even though I was still really hurt, but she refused to talk to me. True story. This was our first big fight ever, and I couldn't believe our friendship was that fragile.
In hindsight I can see this friendship was not healthy and it's a good thing it is gone from my life. And I learned from the mistakes I made during the argument. I think I will handle any future conflicts with friends more maturely.
I hope you can have a quiet, loving, tearful, honest talk with your sister about how happy you are for her, and share what you are going through.