Is this classed as bullying?

[malica]

Having done it just once and never again is not bullying. Bullying is the ongoing terrorizing of another. You don't have to necessarily insult someone to bully them - you can threaten them or say any number of other things which could be considered bullying... if they were ongoing. A single incidence of insult/disagreements does not equate to bullying.

I suggest you apologize for whatever it is you said which was not correct (e.g. you don't need to apologize for disagreeing with her, but do apologize if you used a condescending tone, etc) and stay clear of her since her mother is one of "those" mothers.