Wasn't her "ace" her Morpeko? Her Grimmsnarl may be gigantamax, but her Morpeko is the one constantly by her side.
I'd argue Morpeko is her "signature", it's the thing she's best known for, while the "ace" just is her strongest mon. For most the ace and signature are one and the same, but for others they might be different.
Like Pikachu being Ash's signature but Greninja being his ace.