Sit down with this person and explain just why you lied and why it was in their best interest. Sometimes in life you have to tell a white lie to protect someone or just for their honor. I know it feels bad but "white" lies aren't all that bad. Sounds like you need to have a heart to heart talk with her and I'll bet good money that everything will be fine afterwards ! :)
All I will add to Rooster's advice is:
Unless THEY believe it was "for a good reason" ... Whether you believe it was or not, doesn't matter.
Quit lieing to them, apologise to them and don't do it again.
You have to explain why you lied because you don't trust somebody just a little bit you either trust or you don't and that trust was shattered when you lied.
You have to hope they will agree that you weren't honest with them for a good reason and you should lose no time in sitting down with this person and having a long talk.
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