I think if I had a broken M9 I might throw $1000 at it to get it fixed if I was really in love with it. I look at things as a zero sum regardless of how much I've already invested in it, so the cost of having a working camera again would be the cost of the repair factoring in what the camera would sell for being inoperable. If the camera is worth $1000 as is, and the repair is $1000 then the actual cost of the repair would be $2000. You might want to talk to her to see what she really sees herself doing in the future. Maybe it is time to move on. Your hesitation says a lot too and I don't blame you.
If she likes the Leica then she might dig the Fuji XPro series which would be ergonomically nearly the same. Sensors aren't full frame though so if she wants to continue using Leica glass that would be a consideration. Fuji does perhaps the best color which is a big plus. If I were starting from scratch and wanted to just get a digital camera for myself I'd get a Fuji. Keep in mind mirrorless cameras, which is pretty much everything these days, all have electronic viewfinders. She might really hate that. The XPros have an optical finder if I am not mistaken.
If she wants to keep using Leica glass then maybe a newer Leica would work. Don't know what they cost though.
Hope that helps...