If you are going to enter a philosophical debate on the proposition, "Your neighbor is beating his wife," then you absolutely should be prepared to defend your side. This is the difference between a courtroom trial and a philosophical debate. A courtroom that presumes innocence until proven guilty relieves the accused of the burden of proving his innocence, but, in philosophy, it doesn't work that way. You can't say, "I'm right just because nobody proved me wrong," in a philosophical debate. You are going to get called out as committing a logical fallacy of Argument from Ignorance.
Atheism isn't a debatable position. You can argue for some form of theism if you like, but no return argument is needed from the atheist, who needs do no more that say that he isn't convinced.
I agree with you that 'you lack a belief that gods exist'.
And that makes her an atheist. What debate are you looking for? What claim do you think the atheist is making that needs defending? That he or she isn't convinced by any theistic argument? That's my position, and it isn't important to me that anybody believe me when I say that about myself. Therefore, I have no burden of proof regarding my unbelief.
Isn't atheism an idealized refusal to "believe in" the existence of gods?
Skepticism is the refusal to believe anything that is not adequately supported. Atheism is the result of skepticism applied to god claims.