Rosalina would not reset the universe over a petty scrap, but I also don't think it would ever come to that against any of the cast. Like I said, she still controls gravity, can teleport, fly, summon a rain of shooting stars (i.e. a lethally hot substance), etc.
And like you said before, the character in Smash is, technically, Rosalina & Luma. So we actually should consider what they bring to the table for her:
-Lumas can transform into health expanding mushrooms, as well as 1-Up Mushrooms. Even if you assume Rosalina to be mortal, the Lumas could give her a stock of extra lives and heal her.
-Lumas can direct Prankster Comets.
-Lumas can become planets, galaxies, Power Stars, Grand Stars, Comets, etc, all of which could be utilised by Rosalina (for example, a Power Star provides her with a Final Smash in Smash Bros, and in Smash Bros, it's actually the strongest Final Smash by far in terms of raw damage output potential - if you could use it against the Hands, you could nearly one-shot them).
-They can fight hand to hand and are actually quite strong (even Palutena highlights this in Smash).
-Rosalina can summon all kinds of Lumas at will from all across the cosmos:
So basically, Rosalina is essentially invincible even if you assume she has no deity powers and is mortal - the Lumas can grant her effective immortality anyway, and they can offer so much offensive power too.