The biggest thing about Asuna, is that she has the opposite ability of magic users, she has the ability to cancel magic.

She can deflect and dispel any magic spells cast on her and she can destroy any magical barriers with her fist or her swords.

The limitations to her Magic Cancel is her ignorance with her ability (in this case, instead of completely dispelling magic, her clothes tend to vanish and/or explode) and if the environment around her was already spelled.