"Love bites" other wise known as hickeys can happen without even experimenting with necking and so on. One of the things that was popular when I was between the ages of 10 - 18 was "indian burns" - pinching and rubbing the skin to make a fake hicky. and also self sucking my mouth, with straws and so on on the skin to create hickys.

Your daughter may not nave done anything wrong.

When my child at 9 years old came home from playing outside with his friends with what looked like a love bite I sat him down and told him that sucking on the skin and creating love bites is basically breaking the blood vessels under the skin and I would rather he not damage his skin that way. he told me that a friend had one and so he allowed his friend to pinch his neck so that he would have a hicky too. but now that he knows doing that makes him bleed under his skin and is what a hicky is he would not do it again.