Wow - that sounds intense. It sounds like she is scared. I think we sometimes do not understand how scared kids can get over things, and how primal that fear can feel. My daughter had a similar reaction over pooping in the potty - for whatever reason, it was so scary to her that she could not deal. What was helpful was a combination of strong encouragement and backing off. Sounds contradictory, doesn't it? But it is not. I believe the key is to give your daughter the absolute last word in whether or not she gets in the tub, and how long she stays there. (Really - if she is in water all the time outside, how filthy can she be?) BUT: offer the tub to her every night. At this point, you are probably dreading the bath time experience as much as she is right now, so pay extra attention to presenting it as "no big deal". Do not show the least bit of apprehension, because she will feel it and it will feed her fear. Stay completely calm. Be matter of fact and upbeat about bath time, but acknowledge that you see she is afraid. Reassure her, and encourage her to "try". If that means she is willing to get in the tub, but then wants to be out in less than 30 seconds, consider that a success. If that means she does not get her head wet, then so be it. And talk up any success to her: "Wow - you did it! You took a bath even when you felt scared!" But DON'T force her. And if she chooses to not get in the tub at all, then your job is to say OK, and move on matter of factly to the next thing. Forcing her will only make her sense of panic more intense. You may have noticed that she cannot hear you or take in information when she is that scared. Making her take a bath in that state will actually make the process take longer. It might help for you to tell yourself that this isn't about bath time as much as it is about helping her work through a fear.
When I tried these things with my daughter around the pooping, she spent a long time resisting the potty. But she would "try" almost every day. One day she pooped on the potty, and her pride was off the charts. Not only did she poop on the potty, but she overcame her fear entirely. And she knew it, and she felt GREAT! She's never had a problem since.
Hang in there!