Yeah, sometimes people are crazy about stuff like that. You'd think she would know that she needs more than one quilt/blankie for the baby and it's not always going to be used in the same room.
Had a friend whose did the pottery barn thing for a boy with the sailboats and stuff. I just asked her what the decor was and she told me and I made a little sailboat quilt out of the same colors. She loved it but I wouldn't make one for your SIL as I'm sure she wouldn't appreciate it.