Damn, I might have to buy those cards even if I don't get the game. I always dismissed print merchandise when it came to completing my Rosalina collection since it's usually just stock art of her put onto a trading card or something, but this is mostly new artwork and they function as amiibo.
But yeah, she looks great and her stats are godlike.
EDIT: I had a closer look at Rosalina's stats as well as other characters, and have been able to somewhat deduce how she fares in each sport.
Keep in mind, we don't have every character's card yet (such as the horse racing one for Rosalina), but we have most of them. Also, I'm basing my comments on how many blocks Rosalina is missing out of the total possible stat blocks altogether. I actually can't tell what each stat is from the images. And I don't know how much of a difference each one makes or how much difference a single block makes. So this isn't a definitive ranking.
Tennis: Star/Superstar Rosalina seems to be objectively the best character in Tennis. She's only missing 4 blocks, having all of her stats near maxed out. The next best character so far, Yoshi, is missing 8 blocks. Everyone else seems to be missing 10 blocks, if not more. A similar thing applies when comparing the base versions of the characters. Rosalina still has more total blocks filled up, though Bowser and Donkey Kong are pretty close. Basically, Rosalina is the Tennis Queen. It's no wonder one of the banners in Tennis advertises "Rosalina's Tennis School"!
Soccer: For Soccer, the Superstar versions of the characters are all missing 4 blocks, with the blocks they have being distributed a little differently. So Rosalina is actually just as good as anyone else here. The same applies to her normal version.
Baseball: Most of the Superstar cast is missing 10 blocks in Baseball, including Rosalina. The only exceptions are Diddy Kong and Baby Luigi, who are missing 9 blocks, and Mario, who is missing 11 blocks. So she's a little better than Mario, while Diddy Kong and Baby Luigi are a little better than her. Everyone else is just as good. Same applies to normal versions of characters, except Mario is just as good as everyone else. Diddy Kong and Baby Luigi still have an extra block.
Golf: Going solely by the stat block totals, Rosalina is unfortunately the worst character in Golf. She has a measly 11 blocks filled in for both her regular and Superstar form. Everyone else has at LEAST 15 blocks filled in, with some going even higher. However, it is worth noting that Rosalina is the only character to completely fill up a stat in Golf, so far. However, other characters almost fill that up anyway, so they're probably ultimately better choices. Unless that one stat Rosalina has filled up REALLY makes a difference, then I'm afraid you're better off using any other character. I actually find this really strange, since I hear Rosalina was one of the best in World Tour (she'd want to be, since she was DLC). Kinda weird how they nerfed her so hard for this one.
And here's her Golf stats, in case anyone hasn't seen them: