I don't know how so many snarky comments are getting upvoted here. Barely an ounce of empathy to be found in this entire comment section.
It isn't hard to understand why you'd focus on the content of the essay rather than the mechanical process of typing it out. Clearly you're letting her type shorter things, so she's gonna get better over time even if you type for her on these longer essays for the moment.
Sorry you lost the essay. But I'll look on the bright side and say it sounds like you're doing a fine job working with your kid on their homework, and ideally this is just a growing pain as you use FOSS in the course of their education. I use LibreOffice too and am sometimes similarly frustrated at unintuitive or unexpected design choices.
I think OP has explained that he does let her type when it's a shorter document. Which I think is perfectly reasonable at this age.
I couldn't type very well until I took a dedicated typing class at school when I was 13. By the end of the semester, I was faster than 95% of all typists worldwide. Maybe OP's kid might be interested in a class like that next year. And if not, she'll still get better over time even if she isn't typing these long essays right now.
Basically, give her (and OP) a break. They're doing fine.
Edit: also, I don't think you're an asshole for offering your input. Nothing wrong with that. It just comes off as a bit overly judgemental given OP is guilty of... occasionally typing his daughter's longer essays to save time (a finite resource that any parent has a limited quantity of).