From my experience fighting Rosalina & Luma, Meta Knight's Drill Rush (side special) is quite an effective method to take Luma off stage, giving you time to take on Rosalina by her self. I'm unsure of this has been mentioned anywhere but its something handy to know.
When Rosalina shields, Luma doesn't leaving it open to death. I would suggest drilling into the ground once you are near the edge though to bounce off to avoid potential punish or falling off!
When Rosalina shields, Luma doesn't leaving it open to death. I would suggest drilling into the ground once you are near the edge though to bounce off to avoid potential punish or falling off!