Personally, I think e-bike conversion kits are not worth it. The price isn’t super competitive with just buying a cheap e-bike, installation can be a real bear, and it might necessitate upgrading other components on the bike (like the brakes: ebikes + caliper brakes is a recipe for a bad time).

If your spouse is going to be commuting daily, has disability issues, and hasn’t previously commuted by bike, I would definitely get an e-bike. I usually recommend two brands: Tern and Ride1Up. (I’m assuming, perhaps incorrectly, that you’re in North America, if not, disregard.)

Tern is the pricier option, but they have really good components. I personally think the HSD is the one I’d go with.

Ride1Up has, I think, the best budget e-bikes in the US. Their Roadster is a great “stealth” option, if you don’t want something that looks like an e-bike (and is not super heavy). The Portola folds up and is super-adjustable for different rider sizes.

One thing I will mention, is that a lot of e-bikes with built-in rear cargo racks usually have passenger packages, which, depending on you and your spouse’s weights might be a great option for getting around town together. My spouse and I usually take the single e-bike for in-town trips, with her riding on the back.

My stable of bikes between the two of us is two regular bikes and one e-bike with a passenger kit. For my regular bikes I picked them up off facebook marketplace/craigslist. I’m reasonably certain that neither was stolen. I think the most important thing to look for in a bike is fit, seating position, and hand position. An upright seating position is easier on my back, but is less efficient than the typical bent over position. In urban cycling it also keeps your head higher for scanning the road. The nice thing about bikes is that, generally, you can alter them a lot once you get them, so as long as the frame is the right size, you can usually tinker with it to get it set up how you want.

Buy lights and a good u-lock. Have fun!