The kind of ditzy, cheery girl Undyne had spoken to before also proved to be a formidable fighter. She didn't have Undyne's raw strength, but she was flexible and quick, and was able to twist out of the arm pin before she could get a proper grip. She countered with an expert leg sweep that would have been very effective on dry land where you can't just float.

It was pretty clear that while she was a skilled fighter, she was also not used to fighting under water at ALL.