Male sure you actually have her checked as a builder. And maybe you could put one of the other villagers to fix the the hut (again check building) to get just a notch of building skill. That will mean he/she too will water the field without supervision.
I usually take the opportunity while the lagoon is being unblocked to put each villager to clear one or two rocks, so they get the smidgeon of experience to so I can use them to water the field later on if I need an extra hand