Sally will be jealous at first, but then she will get to know the new puppy and they will probably become good friends.
Just let them get to know each other on their own terms, and make sure you pay lots of attention to Sally so that she doesn't feel left out.
As for advice, make sure your sister-in-law provides a crate and pee pads (unless you're outdoor training), food, treats, toys and chewies. She may want to leave some Nutrical with you just in case of an emergency.
I think it's wonderful that your sister-in-law has someone to care for her new puppy while she is at work!