I agree with 60/40.
Rosalina can outrange Luigi bad, and Luma is just..... what? Heck, how many times my Fireballs has pelted his tiny body yet it STILL not dead? Thank the 52 HP for that.
However, aside from Rosalina's obvious advantages, Luigi can also harrass Rosalina bad. His Cyclone, while it leaves him vunerable, can take the Luma with him, and is his punish options. Spotdodge, punished. Roll, punished. Shield is your only option.
Oh, and if he takes away the Luma, Rosalina is much more vunerable to his approach, and there is ALWAYS an unwritten rule when fighting Luigi, unless you are Master/Crazy Hand or Master Core (Except Master Shadow), and that is......
AT ALL FREAKING COST, DO NOT GIT GRABBED!
Luigi racks up damage like no one's business, and his attacks are all quick. Get grabbed at 0%, 24% guaranteed. Plus, his aerials are much faster than Rosalina's, and thanks to Rosalina's tall frame and floatiness, Luigi can control the air as long as he attacks quick enough.
And another thing, he has tons of KO moves. He is very unpredictable also. Plus, Rosalina is a deadly combination of tall, light yet floaty. Luigi's B-air is his insta-smash attack in the air, as long as he sweetspot it.
Overall, Rosalina must keep Luigi under control and don't fall to his tricks. He want you to approach him, and if he manages to get in, he is scary. Rosalina wins because she has better mobility and range, and also great recovery that is almost ungimpable by Luigi, and her juggling hits hard.
However, she must be careful when gimping Luigi, hitting him while he is using Green Missile won't work as long as he has his double jump. Gimp his Luigi Cyclone, and he is almost likely not coming back. However, gimping Luigi Cyclone IS a problem, considering on how fast and high he rises. Just don't get caught in that Cyclone.
60/40 in Rosalina's favor IMO. Due to her advantages over him, and Luma is preventing him from getting in. But when he gets in.....
I cannot imagine.