My other half has ET return next week and (forgetting about potential strike right now) for the return I just saw CE redemption segment available and booked this for her. The ET return is cheap one and non-refund. Will there be an issue she is booked twice on that return flight? I understand that theoretically she needs to fly the return leg of the economy return, but more generally speaking is being booked twice on same flight going to cause issue? Will system see this as error etc.

I think I have been double booked couple times, but cannot remember the details.

Thanks!