My SIL is a maternity ward nurse and thinks she knows EVERYTHING...?

She sounds like she might be a little jealous, especially if she's constantly around babies without any of her own yet. Those kinds of people just suck. I wouldn't go to her with anymore questions then if she acts sad about it again simply say that you know she knows a lot about it but you need advice from people who've experienced it because not every pregnancy goes by the book, that way you get your point across but without being mean about it. Good luck. She doesn't sound fun...