You wife has an exceptional and lovely voice. She would benefit from working with a producer or engineer who will be honest with her to improve the VERY few areas in which her intonation isn't hitting the mark. It's very clear she's got the ear and musculature to sing well and hit her targets, so these little micro areas are likely just things she didn't notice.
A good engineer or producer will have the ear to flag these moments and get a do-over, which will ultimately pull a flawless performance out of an exceptional singer. This is how it's done on a pro-level, most singers don't always do a flawless performance in one take and we all need someone behind the glass who will say "let's try that one again."
Many so-called producers are not up to the task because they don't have the ear for it.
I only mention this because it's clear she has the talent to do this exceptionally well, and a lot of people will blow smoke and tell you she's perfect. She very nearly is, but finding a producer worthy of her talents is your real challenge here.
Best of luck!
Thank you so much for the feedback, we really need to hear this. I'm the guy right now who's doing that and I know I'm not catching everything.
This all started out as a lark as I'm recently retired and wanted to add to the hobby list. But the positive comments we've received over the songs the past year made me realize this could be larger than just us making fun recordings. And maybe not, we'll see which way the wind is blowing from this point on.
Yours is the kind of comment we've been looking for, and my wife asked me to thank you for it!