this was going to be my suggestion. Google allows you to set up rules-based forwarding too, so, say, only forward emails that include ‘eTicket and receipt’ in the subject line to [wife address], or only emails from ‘@united.com’. Just to be clear, before you can set this up, requires opt-in from the address you are forwarding to.

As for where UA itineraries go, IME, that can be a bit tricky with multiple emails. Sometimes, I send booked itineraries to my own address, and some to a joint address I share with my wife, if it’s a family trip. Problem is, UA seems to randomly ignore which address an individual itinerary is suppose to go to, and sometimes, with the link on the site if it’s already been purchased, goes to the address it shouldn’t. Honestly, I’ve given up trying to figure it out.