Kid kissed my baby on the lips

I have an 8 week old baby, and I also have 3 nieces. My youngest niece is 4, and from day one we have set boundaries about no kissing on the face with everyone including my nieces …. I’ve repeatedly have had to tell my niece not to kiss my baby on the face and today she kissed her on the lips and I wasn’t fast enough to stop it. My sister in law (the mother) tries to tell her to stop… but she’ll usually only correct her if I say something first to her. It’s just infuriating because my niece is in daycare and can pass on anything to my newborn. And now I’m stuck with crippling paranoia and anxiety about my babies well being I just kind of needed a rant.