What type of ticket did you buy, and for which route?
For SBB supersaver tickets you can request a refund if you bought a duplicate ticket. See here: https://www.sbb.ch/en/help-and-contact/refunds-compensation/refunds-compensation/refund-form.html
So request on refund, and buy a separate ticket for your wife. Electronic tickets must contain the name of the person travelling, and once issued that name cannot be changed.
Note that you can buy multiple tickets for different persons at the same time just by adding them as passengers. I do that quite often. When you purchase a ticket you will notice that next to your name there is a little pencil icon. There you can add more passengers if you want. The site remembers this, and that will make it easier to buy multiple tickets in the future.