Say something and have them have hurt feelings?

Recently we were at our families house and my SIL, who’s in hs, had something on her lip. To be honest it looked like herpes to me! I asked her what it was and she said a pimple!!

Which that could be the case but it didn’t look like a regular pimple and was on her actual lip.

I didn’t want her touching my daughter and she usually kisses my daughter on the cheek but told her to not kiss her.

I didn’t want to hurt her feelings but I rather her had hurt feelings than my baby getting mouth herpes!!

What do you guys do in this situation?

Say nothing and risk your kid getting something permanent or say something and let them have hurt feelings?