Aha, the answer to this is such a given that I'm not even going to mention her name.
I think the reason she was so fun... okay, not fun, but interesting to train in FR/LG was mostly because by that point, she had established herself as my favorite, unlike back in the days of the original R/B where that honor went to Vulpix, who by the way, I never had on my team. Go figure.
Determination to basically win with Nidorina... oops. Ah well, determination to win with Nidorina at the top of the command chain and then call it a day was all I had left, as I was pretty tired of the games by the time FR/LG came out. I forgot if I ever completed the island side quest after the game. I remember there being some Rockets and some Johto Pokemon, but I have no idea what any of it was about anymore.
The only thing that's ever held true since FR/LG or Emerald is that I will only play the games if I can play with my favorites, which wasn't a method I used just one game prior in R/S and all games earlier. Kind of interesting given how quickly I shifted.