when relationship of both A & B go deeper, I think it is advisable to tell the truth, because A can't keep the secret forever because she has to think another lie to covered up the previous lie..as the list goes on, so wait till the relationship go deeper (both understanding each other and mature), then tell it because it is good for both party.

ya...

"10 cups is not enough cover 11 eggs"

do remember the chinese folks said