Before this movie we aren’t given any indication Leia was ever anything close to a Jedi, she seemed to be in the same place we left her in RotJ, naturally in tune with the Force without any formal training, her space walk in TLJ is closer to Luke pulling the lightsaber on the Wampa cave, which he did before any real Jedi training. It would’ve been fine if they stuck to that but in TROS she suddenly had all this Jedi training that she chose to never use, so there needs to be a reason for that. The film decided the reason was that if she picked up a lightsaber her son would die, which is ridiculous, so I think there needs to be something equivalent to replace that.
I guess I’m having a hard time understanding why you aren’t okay with reverting back to the idea that she didn’t get much formal training, then? We already shot down your point that then she couldn’t have trained Rey - she didn’t really train her, just mentored her and wanted her to reach the past Jedi instead of her.
We can argue semantics all you want, but the movie is very explicit that Leia is supposed to be training Rey, full stop, I don’t think anyone could watch those opening scenes and come to any other conclusion, she literally calls her Master. And the whole point of that flashback scene is to explain how she could be training Rey, it’s convoluted and messy, but it’s stylistically designed to be that way, and you can’t undo that. Even if you remove being the “last night of her training”, she still needs to have trained enough to be able to teach Rey, otherwise none of it makes sense.