Yeah, my bad. Sorry.

Yes, I think it makes sense at some point that Ultimecia created Griever because she thought it was the strongest creature, but I still find that hard to believe because:

Rinoa: So that's what you call it. You know Zell said he'll make me one
exactly like it. Who knows, maybe I can become like a lion, too. That'd
be crazy, huh!? I mean, everyone might, y'know, get the wrong idea
about us.
See the bold part? She says she can become a lion (Griever), and yet in the end Ultimecia transformed herself into Griever (created it).

Let me re-cap, at the time when she says that. She wasn't possessed and is still on White Wings (good) and she said the 'lion' word because it's supposed to represent a good defense or something like that. On the other side, Ultimecia is on Black Wings (Evil) and she created Griever to represent a bad defense towards the Squall and his party in the end because she was "evil", you know what I mean. It's weird and hard to believe that Ultimeca picked Griever out of random because she thinks it's the strongest.

and also I think that, in general, Griever isn't the strongest, Squall only thinks that, not others.

Anyway, I'm not exactly sure how Ultimecia read people minds, I thought they need to be possessed first. What I mean is that if Ultimecia actually read EVERYBODY's minds at all the time, surely she will know what Squall is thinking of how to beat her in that battle? And surely she could have stopped that?