Nah, Rosalina is great on Norfair. With the Luma you can super easily control an entire platform, and if people dare reside on the platform above you, you can make life hell. Sure the lava can kill Luma, but don't get hit and it's all good unless it's the background wave but if you can't win the battle for that little house as Rosalina you are doing something very wrong and it doesn't even come that often so whatever. The geography actually helps you whereas it screws up a lot of other characters; that's the main thing to take away from Norfair. I mean, Norfair was legal in my region in Brawl forever and was my main CP and I'm super comfortable on the stage so that's definitely a part of it, but I feel like it does more for me as Rosalina than it ever did for me as G&W and it won me a lot of games as Brawl G&W. This isn't even an argument for Norfair's legality (I think it actually plays a bit worse than it did in Brawl and I'm more concerned with saying no to bad bans like Skyloft/Wuhu/Windy/PS2 than more reasonable ones like Norfair), but hey, if someone offers me Norfair in tournament and their name isn't Thinkaman I'll probably accept.
In other words, there isn't really any stage even among the banned ones I actually fear as Rosalina. Pac-Land would probably be the worst and Wily Castle/Pyrosphere would annoy me a lot but even then I'd keep the faith in the Rosalina probably and would be sure to keep my patience game in full swing. Those three stages have about a 0% chance of being legal at any possible tournament even a super liberal one though so I'm not exactly concerned about them. The ironic part is that, while I like transforming stages, I probably camp on them a tiny bit less on average just because of the way they force more movement; I don't enjoy playing on only SV but if I have to expect some serious turtle mode.