I hope you would stick up for the coworker. Be calm but point out what she has done and let her know that you appreciate her work. I would also, if possible, or necessary, meet with your supervisor and express your hope that this can be resolved in the interest of creating a more healthy/productive work environment. If she targets one person, it can turn to another...maybe the supervisor is stressed and this is what she tends to do...if lucky, she doesn't feel good about it later.