My motherinlaw is healing from a coldsore touched my 6wk old babys cheeks after washing her hands. Is my baby safe? I wiped her cheeks with water after?

Probably. Good handwashing often removes clinging germs and viruses. Most everyone eventually gets the cold sore virus. Herpangina is the name of the condition of a first time infection and is associated with fever and painful mouth sores. Usually passes in 5-7 days. Encourage adults with active lesions to avoid direct contact - like kissing in cheeks - during their flare up. Situation sounds low risk.