Ruminant
Thanks again for your time and patience.
You will be surprised to hear that I discovered the existence of that Branden book only 3 weeks ago. it is not readily available at my library (in Australia), I do seriously want to buy that book soon though. It looks a classic I should’ve purchased ages ago.

re your issue
Seems this girl has least improved under your wing. (at least opened up to you)
Any way of grading her tasks from doable to slightly challenging to more challenging?
Time for a heart to heart? One of those tough conversations, where you need to be honest about your own feelings “Look I’m trying to help you but you don’t seem to be taking initiative. Do you want to do this or not?”
Any way of throwing her in the deep end and letting her make mistakes?
This is what I wish my manager said to me ” Jack , the only way you are going to learn is get in there and fail, without anyone to catch you. We’ve all made mistakes so I encourage you to have a go. Try to believe in yourself!”
Then maybe I am expecting my manager to be a kind of nurturing teacher. I can’t expect her to care about my progress. She has to worry about the big picture. Getting the job done!
I’m not sure exactly your context so my advice might be way off the mark.
Thanks again.