Welcome @rjlundy1, I know it must be frustrating trying to figure out how your daughter got the infection. The Centers for Disease Control has some information that possibly will answer any questions you might have.

"Common in Young Children -- Hand, foot, and mouth disease is common in children under 5 years old, but anyone can get it. The illness is usually not serious, but it is very contagious. It spreads quickly at schools and day care centers."
-- Hand, Foot, and Mouth Disease | CDC: https://www.cdc.gov/hand-foot-mouth/index.html

Does your daughter go to a day care center or school where she might have gotten the disease?