Sister in law trouble and being pregnant

But before they announced it, she walked in the door at my parents house while I was drinking a very small glass of Pepsi. I've been drinking loads of water so I didn't think it was a big deal. Anyway, she walks in and goes "oh my gosh! Caffeine can cause a miscarriage!" 

I was furious. Why would you tell a pregnant woman that?! I'm already worried about a miscarriage since my sister had one last fall. Id think she would know how I feel being pregnant too. But she got pregnant the first try and has no family history of problems with pregnancies...unlike me who took five months to get pregnant and has a lot of miscarriages in my family history.

I thought it was extremely rude and was a no brainer to not say that. I want to enjoy our pregnancies together but this is the second time she's made a comment like that. The first time was right after we announced it. What do I do???