Visitors of baby with oral herpes?? Question?

Kirsten
After reading an article recently that a 1 month old baby contracted oral herpes from a visitor who kissed them on their face/mouth, I'm slightly freaked out!! This visitor did not have an active outbreak, so there was no way for mom to know. Plus, I never knew that oral herpes is potentially life threatening to infants, can cause brain damage, etc. 
How do I politely ensure that no one kiss our baby's face but US? The kicker in this situation is that my MIL has oral herpes, and if I tell her she can't kiss her grandson on the face she may kill me....