Hitting and biting back is not okay. Doing that shows the child its okay.Tell the child no, that hurts. Get the child involved in an activity, redirect their attention. Use time outs or time ins if necessary.
Don't do it back to her, that's child abuse! My son who's turning 18 used to do that as a toddler! I'm telling you from experience, she will stop on her own! If you ignore it, she's not getting attention from doing it & she will stop! Try playing with her more, it's a play for attention! Something's missing in her little life!
Do the same back to her, I'm not saying you use full force but you need to get her attention. As far as this child abuse crap, that's b.s. My niece used to bite and spit, I've seen her pediatrician bite her and spit back at her, right between her eyes, It was quite a shock!
Don't do it back to her; that would be abusive and wrong. Adults must not behave this way. Remove her from closeness with you when this happens. Then try to identify the triggers for this behaviour. What makes her this angry? Please remember that this is a phase that will pass as soon as she is able to structure ideas into a few words and is understood by others.