I don't know what Miss Sadie's personality is, but my sheltie Buffy is great with babies. Sounds like most shelties are. However, if you are in doubt maybe you could keep her on a leash around the baby and give her a treat if she acts appropriately. Also, it might be a good idea to only have them together for short times. Even though Buffy is good with babies we always supervise her with my niece or my friend's baby.
There are classes about preparing a dog for a baby around my area. You may want to look into this or consult with a trainer if you run into issues.