You weren't dating, its none of her business. You can say this nicely, but that's it in a nutshell.
Guys lie about stuff all the time. Usually small, stupid stuff that doesn't really matter. So do girls, tho they will deny it. Which is ironic, of course. The difference is that guys don't get their knickers in a knot over it.
Tell her that you won't lie about anything really important, but that the world runs on white lies. Its what keeps civilization *civil*. If she disagrees, tell her to grow up and think about things rather than believe what she sees on television.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh