Lets be honest here, the power company doesn't turn off the power if you are a couple days late. I've never faced that issue, but I imagine that we are looking at being at least a couple weeks delinquent. The technician likely got a list of houses in the morning, some time between when he got his list and when he reached her house, she paid. Hardly the poor guy's fault.
I pay bills online all the time, and I don't recall ever getting an e-mail with a confirmation number when a bill is paid. Also, it is fairly uncommon for a payment to go through on the same day, so it hardly surprising that the technician was suspicious of her e-mail.