Didn't Ursula evolve two Eevee during a Contest?They've never shown an on-screen Stone evolution that the trainer does on its Pokémon on purpose. Even though Lillie got an Ice Stone, she never used it. Clemont does mention in the Geosenge Town episode that he used a Thunder Stone on his Helioptile in the past (obviously) but it was never shown on-screen. The two Stone evolutions we've had, Lombre into Ludicolo and Poliwhirl into Politoed, both happened by accident. I think the writers don't want to show a Stone evolution on screen that the trainer decides to do, because it might come across as the trainer forcing the Pokémon to evolve. In fact, I bet if Lillie does ever appear again, she'll already have Ninetales. They wouldn't dare ever show her deciding to force Snowy to evolve. Prob the same reason Sandy never evolved either. It feels like an unwritten rule in the anime that they'll never have a trainer decide to do that tbh. If it ever does happen, I bet it'll be the plot of an entire episode, showing the trainer and Pokémon agonizingly keeping on changing their minds back and forth until finally deciding to do it, and act like it's some dramatic tough decision.
Why the **** do you hold a grudge against a Pokémon whose fault it's not? It's shitty writing dude, not a shitty Pokémon. She could be redeemed if she ever appeared again.