Oh---this is so nice but sorry for your loss. I'm sure it was a comfort for your friend to know her bird would have a safe place to go. Well, I'm sure you know about quarantining for 45 days in another part of the house. If either bird is vocal the other bird will hear it and sometimes make sounds in reply. In other words, they hear each other & will become aware of each other. After that, I place the cages in the same room w/o letting the new bird out unless it's w me, however, I won't let my resident birds climb onto the new pets cage (only my macaw will attempt this).
Then just take it day by day. It can take a couple of months for birds to get used to each other and if they both get handled regularly you may have to do it while one remains locked in the cage. You will be the best judge of how they are getting along & will figure out what to do accordingly, I'm sure. Hopefully they will settle in together and (at worst) just stay on their own cages when out unless you're handling them. That's how it's always worked for me & I've made many introductions over the years. I'm sure it'll work out fine =: ]