Ha, I'd be the first to sign up if there was a skill building course of some kind here!
Thank you all for the important tips! We're going to practise shifting today, I just need to find an empty playground or something. Flat pavement only

There was some solid progress so far - the first day she was even struggling to get on the bike and was getting off by jumping to the side. However, she started reading up on the proper technique and the next day she got the hang of it. She even positioned her seat properly and it was a vast improvement.

We did since go to a park with very mild, short ascents and descents (only a couple meters of climbing/descending) and she did enjoy it and asked to go again. I tried to explain the correct position and tried to point out how staying off the saddle improves stability when it gets bumpy, but her shifting issues really need work first. She has grip shifters that I thought would be easier, but she keeps using the front derailleur to shift instead of the rear. When she does, she doesn't switch cogs all the way and the chain grates against the derailleur a lot

Basically, we'll just have to work on that a lot before hitting the park again :/