Sister 1 - single for years after two bad relationships
Sister 2 - infertile and husband cheated
Sister 3 (op)- Tragically lost her beautiful daughter to suicide.
OP, first off let offer my deepest sympathies. I am so sorry for your loss.
All three of you have been through the ringer. You've all got significant trauma and loss.
I have found in my own life, when people feel heard it helps them move on. Feeling validated is such a gift to each other. Given you thought she was happily single for many years it seems this was a rare bit of emotional honesty she was sharing. That can be hard and she probably felt shut down by you. As though she's not allowed to hurt because you hurt more.
I HATE what she said to you. That was awful and not ok. I can't even imagining thinking that way. She owes you an apology.
Your second sister might be wrestling with her own place in this. She wanted children. Infertility involves it's own private hell.
I think you could all be a huge support to each other. You've all been through a lot. You could be eachothers biggest cheerleaders. 💝