Just some things to consider:
Is the temperature of the water too hot/too cold?
Is the sound of the running or draining water scrary to her?
Maybe bathtime is too close to bedtime and she's tired & cranky?
Is she overly sensative to the smell of the bath products that you are using?
Has she discovered that the sound of her raised voice gets a reaction from you?
Here's some suggestions that maybe your haven't tried yet (or maybe you have) . . .
Distract her by singing songs, making silly faces and doing silly things. For this to work, you have to be really animated and a downright clown. It will make the whole bath thing fun for her.
California Baby has 2 all natural bubble baths that have chamomile and lavendar in them for cranky, tired babies. They smell yummy and will surely relax you at least, if not her. You can buy California Baby at Target and Whole Foods.
Try giving her a bath at another time during the day to see if it is a timing issue. Heck, you can even throw her in there with her bathing suit on and have her believe that the bathtub is a small pool. If you do this a few times, maybe she'll get that bathtime can be as fun as your pool.
Hope these suggestions help.