Although policies differ by airline, United generally will allow people to refund tickets if there was a schedule change of greater than 90 minutes (I wasn't sure if you meant that your wife had a change in HER schedule, or if the airline changed the schedule of when its flight would operate), or at the very least they should be willing to allow you to change the flight to another time or perhaps even another day.
If you just don't show up for a flight, at midnight the ticket will "zero out" and have no value. Since your ticket is worth less than the $150 change fee, you're fine with just "no-showing" or you can ask them to cancel your reservation (not cancel the ticket--this is different). The only reason you might want to cancel the reservation is out of courtesy to the airline, but many people no-show, so you should be fine with just doing that if you want, too. It won't cost you anything to cancel a reservation, but this is different from refunding a ticket (i.e. you won't get any money back).