If you know you are just going to be walking back into a bad relationship then I would not take her back. It will be easier to get over it now and move on then get back into the relationship and then have it end and deal with the heartbreak again. Just keep yourself busy, hang out with friends, do things that make you happy. You will start to feel better with time.
Hope I helped :)How to get over your ex girlfriend?
Someone was being honest and showing true colors and that was her. Even if it was out of anger, she must have had these feelings for quite some time. Also, she has a lack of respect for you because she was going behind your back talking to her ex. If you know that she's the girlfriend from hell, why put yourself through that when you can find someone better? It's hard to let go but in the long run, it'll better for you and you'll have a happier life.