Update!
The impossible happened.
The meeting got canceled due to a couple of last-minute scheduling conflicts.
I couldn't let it go another day without a resolution.
So I called her.
It started off a bit rough. I didn't "lay into her" but I wasn't pulling any punches either. It started off with my explaining that I thought this whole mess was ridiculous, but that I thought the potential of this band warrented at least talking it through before throwing in the towel. (Up until that point she had no idea that this was serious enough that I would consider leaving the band.)
So off we went.
I first asked her to express in her own words what was bugging her. I listened.
Then I explained that nothing I was about to say was personal. Keys guy and I are friendly, but not friends. We don't throw cookouts or double date with the wives or anything. We had no relationship outside of music. But we did respect each other's work and had wanted to be in a band together for years.
Then I laid out my case for keeping him point by point. After the first point, the most amazing thing happened. She said "Well, when you put it that way, it makes sense."
"Hold up. We might be getting somewhere, Twofer. Back off on the attitude and let's see if we can hammer this out" said the voice in my head....or ONE of the voices in my head anyway.
Then I explained another point, and another.
Then I asked if the mystery guy had ever actually WORKED with the keys guy (turns out he had not.)
Both of us lightened up. Both of us laid out exactly how we feel about it. And both of us agreed to move forward WITH the keys guy. (The only condition was that she reeeeeeally wants to sing that dayum Chris Stapleton version of Tennessee Whiskey. Honestly, he does it better but she doesn't suck at it. So I can live with that.)
So, after the first gig, we'll talk again specifically about how well he fits in the band (which I have every reason to believe with be extremely well).
That's fair.
He's in the band. He will never even know we talked. And if he somehow acts like a dipstick I'll have to eat crow and send him packing myself (but I don't think that'll happen).
Situation resolved for now!
Fingers crossed!
Thanks for letting me vent everyone. Your attention and advice has been appreciated.
Now let's go sing some harmonies!