My daughter use to HATE bathtime ever since a year old (she is now 3 1/2 years old). We have turned bathtime into playtime, she gets 30 mins to play (we have various bath toys, half which are just new cheap cooking spoons & little cups I got at the dollar store), we also do bubbles, I sit in the bathroom or in a chair right outside of the bathroom and read a book while she plays. Then around 30 mins we put the toys away, I ask which shampoo she wants (have a variety of tear free from Sam's club), and ask her if she wants we to use the little cup, which takes longer to wet/rinse her hair or the large cup which makes the wet/rinse go a lot quicker. We also have her (or I) hold a wash cloth over her eyes.
If you already do the above... Does her skin look irritated at all, a have know a few kids that due to the bubbles, soap or shampoo or one very rare case the water that would make the skin itch, get very red and not fun for the child. She may have also seen or even just heard from another kid talk about sharks or alligators and she is now afraid (at 3 years kids tend to have something that just scares them, my daughter now is not a fan of heights over 5 ft). If possible do not fill the bathtub just have her in it and wet her down with a cup, soaping up her body and hair then rinse her off. That way you can say that with out standing water there is no way for anything to harm her.
Hope she out grows it quickly for your sack is it is just a phase :)