Don't Want to Offend But.........

Big thing right now.... My sister in law has three kids and she kisses them all on the mouth and that's fine with her kids if that's what she wants to do, but she has said several times that she "can't wait for your baby to get here so I can just kiss its little mouth!" Ummmmm I don't want anyone's lips on my baby's mouth! I love my sister in law and she is wonderful, so I don't want to offend her, but I am already stressing out about confronting the issue eventually!

How do you handle these kinds of situations?