My wife and I are flying from SFO to FLL later this month. Scenario is as follows:

Me: 1K
Wife: No Status

On outbound, we are currently booked in the same PNR with confirmed RPU upgrades.

On return, I need to take an alternative flight to another destination due to work and was going to not use/throwaway the return ticket.

We currently both have RPU's pending for the original return. Wife does not care about the upgrade, but does not want to lose her E+ aisle seat.

Given this info, when is the best time to split the PNR to make sure she doesn't lose her E+ aisle seat?

Many thanks.