Being sassy and back talking can be simply the result of growing older and asserting herself. But, if your daughter is being bullied, she needs some help. I would make an appointment with the school psychologist or the principal to find out what is actually going on. Your daughter needs to learn how to respond when she is being bullied. If she is being overpowered physically, she needs protection. Please do not wait around to see if this problem will go away on its own. There are sources of help for her that vary from school to school. You will need to advocate for her to find the help and make sure she gets it.
Sorry to hear about your struggles - I totally relate. My daughter had a rough few months in school this year, too. I was really worried about how she would remember this time in school. Like any mom, I want her to feel good about herself, have healthy friendships, etc.
Something unexpected became a fun family project that has made her very happy - her yearbook. She's not on just a couple of pages lumped into group photos, but has several pages in her printed copy of the yearbook that are all about her -- her birthday party, her Halloween costume, scans of her favorite artwork, her handwriting, and even pictures from local volunteering that we do as a family. We also included a poem that she was especially pleased with and photos of her best friends.
I loved working on it with her, and our time together was really rewarding. Her school used a new company called TreeRing.com that allows for personalization of each kid's printed copy of the yearbook. Who would think that such a small thing would be so helpful as a family project and as validation that her experience is something to celebrate, even though it was a tough year!