It was in the tips and it was in a pic of the day. Also, after having it happen to you a few times - you should just learn not to grab her while Luma is around, but feel free to when it isn't, especially with its lengthened respawn timer.
It's the same type of adjustments that need to be made towards characters with reflectors - don't use projectiles. Don't use slow readable moves on people with counters. Don't fight Little Mac on the ground. Also, to a lesser extent, don't ever find yourself below a Bowser player, because you're bound to get sat on. It's not that hard.
I'm not saying it was not overpowered, because it very well could be, it's just really early to make that kinda call.
People have yet to even play this game with legitimate controllers which will heighten everyone's play style and quicken response times.
I planned to make Rosalina one of my mains from her announcement but it's just really frustrating to see her getting weakened left and right. Especially when she is already the fourth lightest character in the game and can be KOed very early.
Hope this rumor about her aerial hitboxes being shrank is not true, too.
I'm playing right now, it's so fun! So far I really like Pikachu, Kirby, Greninja, Pacman and Shulk. 
