Shinkansen express and boarding tickets

My wife made a reservation for the Shinkansen. However, she made a mistake and got the time wrong, 2pm instead of 3pm on the day. For the Shinkansen, you need a boarding ticket and a limited express ticket. Since she got the time wrong, she might as well throw away the limited express ticket. Since there was no other way, she bought a limited express ticket again. Not a reserved seat, but a non-reserved seat. I often warn my daughter, but she doesn't say anything about other people.