Apologetic and scared is infinitely preferable to 'whatever' and defiant.
A big plus point is that friend1's mom has most probably came down like a ton of bricks when grounding her culprit, thus paving the way for you to be cool, understanding, mom of the year - your dd will be the envy of her friends and will be more likely to confide in you in future if she's sure that you are not going to rant or be judgemental.
Testing the boundaries is a rite of passage; and it's a fact that sometimes the boundaries get tested by tunnelling under the barrier rather an all out frontal assault, which seems to be the case here.
Rest assured that you haven't raised a liar; your dd got carried away by a not so cunning plan which has blown up in her face, and it sounds very much as if the shock of being found out may be all she needs to not contemplate any repeat.
I would strongly advise you not to ground her; use some of the eminently sensible advice you have been given here to talk through her behaviour and tell her that, even though you may look and feel as old as Methuselah, you understand how difficult the 'between years' that span childhood and adulthood can be.
Explain that it's only natural that she wants to break free from parental rules but that they're in place for a reason, and the reason is that you adore her and you value her safety and wellbeing above anything else.
Please resist the temptation to play the heavy; of course you wanted to 'kill' her when you found out that she'd lied to you, but that's because you are older than her and know that the world can be a dangerous place for defenceless young girls (and boys), and your understandable reaction was in part sparked by your relief that your dd was safe and unharmed.
If you still feel like 'killing' her, do it with kindness and love and lots of understanding and cuddles. Be happy that nothing untoward has happened to her on this occasion, and make it clear that you may not be quite so lenient and understanding if she makes a habit of lying to you.
Once you've made your point, don't belabour it as it may cause your dd to develop a selective hearing disorder.
All's well that ends well, enjoy your weekend!