Since you asked: Ankle-biters describes either cannibals with a foot-fetish or children so badly behaved and brought up that they can't control their physical aggressions. Apart from love-bites — which are only acceptable from strangers after explicit consent — biting other humans on the ankle or elsewhere is a dishonourable form of assault, and to call someone — anyone — a biter is an insulting accusation. Insulting a child has always been seen as an attack on their guardian or parent. You'll have to dig far to find any such negative aspects to cute little singing cartoon people, or people who snap long-obsolete carriage-driving implements (although that one does have bad connotations if you bother to look it up).
My apologies for imagining you knew all that sort of stuff and just wanted confirmation that the term was an acceptable form of ordinary good-humour among strangers. The woman made it clear it was not, and why you ask and explain to us, what you should have to her, illustrates one of the abiding mysteries of humans not getting along. Because they speak before they consider how their words might land, then seek to justify the offence they gave rather than fix it.
It doesn't matter what the term means to you, but what it meant to her.