Ah, I remember the teenage days and how 17 was the worst age.
With that said, you must remember that you are still her mother and she is living under your roof. She must abide by your rules whether she likes it or not. If she screws up, like she just did, there are consequences.
First, I would take Bella to the vet to be checked for injury. Your daughter should be responsible for every penny of that bill if she has to lose her allowance for months. Make her work off the bill doing chores. She will hate it - that's part of being a teenager, but it will teach her some responsibility about pet ownership.
I would not allow her to have Bella alone in her room unsupervised until she has proven she can care for her. Again, she will hate it, but we are talking about a living creature, not something that can be broken and tossed out.
While Bella is living in your house, you will have to be her mommy, not your daughter. She is obviously not responsible enough for pet ownership.
Did her boyfriend consult you before getting her a puppy for Christmas? This is a perfect example of why pets as gifts are such a bad idea.