I had 2 miscarriages between 2 of my children. I would simply say to her ‘whilst I don’t know what you’re going through, I am here to listen if you need to talk’. And then just go back to normal, don’t treat her any differently. And just do something you and her would do ‘as sisters’ together. My sister and I always loved a good dinner and chat. We would laugh and talk about everything.

My sister did too. She never mentioned it to me, except once when she said it was probably a boy. I followed her lead and never raised the subject

My sister miscarried too. She never wanted to talk about it so we didn’t. It all depends on what your sister chooses

yes be there for her and listen. very hard to go through but you will get through it together. maybe plant a tree or something for the baby. something to remember it by

So sorry for your sisters loss.
It really depends on the sort of person she is.
Some people want to talk & get their emotions out, others want to be distracted to take the pain away & grieve on their own.
Tell your sister you’re there for her, in person, on the phone, in a letter.
She is grieving so she may lash out or say unexpected things you just need to remember she’s hurting, she doesn’t mean any nasty things she may say.
Her behaviour may also change.
You’ve never experienced this so it’s impossible to know how she may be feeling.
Try contacting a medical professional to explain your situation and ask them for some advice.
Your sister is going to need support. Being there for her is the best thing you can do. Hold her while she cries. Listen while she yells. Cry with her. You’re allowed to grieve too. But don’t be pushy, she will deal with her emotions in her own time.
I wish you both the best for the future & my condolences during this difficult time.

Sorry to read this. Be there for her. Listen. Sit in silence if that’s what she needs. Just be there (and look after yourself too)