Use a scare tactic... make it known to her that being nasty to you and others will only make it so that she will have to do things on her own since that moment.
Also, I don't think you've explained to her well what anxiety really is. If a person is acting really negatively to it, then that person thinks that anxiety is the worst thing on this planet. You need to convince to her that anxiety is nothing more than just a necessary emotion that is needed for us to survive - without it, we wouldn't be able to make it.
Also, start introducing her to stress management and relaxation techniques. She just needs to calm down. Once she calms down, she will be better.
Good luck!