In either case make sure it will be capable of doing everything she needs it to do. I stumbled across something this summer that caught me off guard since I don't typically teach online. My cousin's daughter is taking classes at my campus and our content management system, Blackboard, has a weird quark. Students can join live lectures with Chromebooks, and iOS devices, but cannot playback the recorded lecture as it requires java. I ended up cobbling together a solution by installing a stripped down version of Ubuntu on her Chromebook to get her through, but what a pain just to take in a few recorded lectures. She is not particularly techie, so I can't wait to get her back on ChomeOS.
Maybe I'm just cheap, but I cannot justify the price increase of the iPadPro over the iPad, but then again for me it has always been a content viewing device that my kids have taken an interest in over the last year or two. I managed to score an incredible deal on a 2018 model over the weekend. Staples had the base model 9.7" iPad on sale for $249, and a $100 off my next purchase coupon showed up with no restrictions, so I picked one up and at $150 it was well worth it. It's a great little device, and I will probably pick up a cheap Bluetooth keyboard to use with it to see if I can truly find a use for it for occasional productivity.
I'll probably tinker a bit with a cheap stylus to see if I find it useful for writing equations and such, but may eventually splurge on an Apple Pencil.
If I were more artistic and had a need to unleash the extra power of the Pro model for some specific work, I would reevaluate, but based on your wife's needs, I wouldn't say that beyond a doubt she needs the pro model.
Good luck with your choice!