when she said you didn't "take care of her", could she mean that
you care less about her, that you were not sensitive of what she
wants? Well... then maybe one day her friend said "just make a
move, it's 2007, don't always wait for guys to do it", which is why
the thing happened.
One thing for sure, she's not really in emotional relationship with
you, it sounds more like "teenager curiosity time" when everyone of
her friends talk about it and she also wants to have the
experience. My suggestion? you have two options: 1. Make use of the
chance and be a bad guy who takes advantage of a lost girl. 2. See
whether you can have a serious relationship with her, and really
get to know each other before taking further step.
Keep in mind, girl who is easy to make a physical move, also easy
to move to other heart.