Just be there if she needs to talk to someone. If not, overly concerned can sometimes create misunderstanding. They are handling the roller coaster of emotions too. Just let them know if they need any help, you are there. I am struggling with infertility too but I don’t like my sister keeps asking me about pregnancy.
It's great that you appreciate your sister who supports you during your pregnancy! There's nothing to feel guilty about because probably it's not the right time for your sister to get pregnant. Just be positive and everything will be okay.
I think what you are doing is already so great. You’re a kind person and I’m sure just your support and empathy helps them a lot. Just keep doing that.
Just keep supporting your sister. Keep being understanding and sensitive to her
Keep trying until successful don’t give up