My SIL really thinks it will be fun to be pregnant together and since my husband spilled the beans that we are trying for a second child she is now too! For me it’s a nightmare! My first pregnancy was uber stressful and full of constant worry for my baby and ended with bed rest and a touch and go delivery. I really don’t want the side by side of a "normal"pregnant woman 
I feel like a total jerk and to top it off she may now be pregnant which makes me feel jealous since we’ve been trying for months and they “just decided to”
That stuff always amazes me…she sounds like the type that gets jealous when someone else gets attention. Let’s face it - you can’t control what she does, but you can communicate to her how difficult your first pregnancy was in case she wasn’t aware or didn’t remember. Let her know that if she also gets pregnant, you may not be able to share in some of the same simple joys as she will side by side, and it will likely be a challenging pregnancy. Maybe once she realizes this isn’t going to be like getting your ears pierced together she will rethink it, but she might go ahead with it too. Don’t project her “normalness” onto yourself, because you are not defective. You have a very difficult disease to manage, and until fairly recently we didn’t have the technology to help pregnant T1 moms carry to term successfully with such good odds. Maybe use this as an opportunity to educate her on that too, and how any child born to a T1 mom is kind of a “wonder baby”, and mom is a wonder too. She may have new respect for you. Good luck with however things turn out!
Thanks talking to her about it that way is a good idea. Hard for me to get a good perspective over my grumpy bitter self sometimes lol