Nana's speed was ridiculously fast. Even with the combined protection of Crimson Edelweiss and the Black Crystal Shield, it would still be difficult for Celine to effectively defend herself.
She did not step backwards because Link was behind her, which would mean that it would inevitably put him in a very dangerous situation. Her only choice was to move slightly sideways in the hopes that she could avoid the brunt of the impact herself.
This confrontation happened within a fraction of a second. Even Vance's reaction time was too slow to do anything, as Mana was still stuck in his Gray Flame wand and the spell just wouldn't form quick enough.
It wasn't that Vance's spellcasting was too slow, it was just that Nana's speed was too terrifyingly fast!
The same was true of the Necromancer swordsman. When Nana and Celine clashed, he was a hundred feet away from them and hadn't even had time to pull out his sword yet.
