Yes, the rule has changed - returns can now be altered after departure.

As you are not Gold, I'm not sure why you'd bother cancelling your wifes ticket. You won't reuse the voucher. You get no Avios back as it was a 241. And the £25 cancellation fee totally wipes out the tax on her ticket.

You might as well keep it in place and guarantee yourself an empty seat next to you on the outbound, assuming you check her in.