Here's the thing a lot of posters here haven't picked up on, that this actually kills 2 birds with 1 stone, but you have to do it correctly.
She is trying to take power back in the relationship and come back into her own energy so to speak, so let her do that by finding the partner for you, let her do all the leg work, let her control the experience, let her set the boundaries, I mean if you go through with the 3some and let her control it, how could she possibly blame you if she doesn't like it?
Here's where this goes wrong: if you approach this from a standpoint of equality... You can have some strange with her oversight but she cannot have some strange with or without yours, so if your approaching this as her husband, your not going to be able to reign her in, you can't just be the husband anymore, now it's time to evolve, now you become the commander, the leader, you set her on the task of finding a 3some and let her find the woman and let her manifest the experience, you are simply an actor in her play, but once you've played your part, you need to find the discipline to get back to your seat as commander, she falls into line once more and you almost role play, have fun with it.
Give her this domain but remember to maintain the boundaries and be the commander, as well as the follower. These days you may also need to set boundaries between the women which is just a whole other thing players really never had to deal with before so you gotta really watch for bad apples and reserve the right to eject any broad for any reason.
Note most of the commentors will say this will fail and they aren't wrong, this is definitely a hail Mary