i have a daughter the same age. and she also slipped and was surprised with a wet face, and then began to scream about baths. (which she previously Loved).
here is what i did.
for the next few baths i got in With her.
i sat her on my lap, and sang her a little made up song, about "now we wash your toes" etc. to the tune of a song she likes.
and i slowly washed her whole body, leaving her head for last, and by then she was calm, and even let me wash her hair. although she was still a little upset with rinsing it.
i did this a few times until she got calm.
then i stayed out of the tub, but right next to her, and without singing, did the same routine .
she remained calm, nut hesitant when i first put her in. i just reasured her a lot, and told her what a good job she was doing.
then i bought her on of those little bath scruby things, like they make for adults for body wash. and she LOVES it.
now i can put her in by herself. she plays the the scrub and has fun again.
so. thats what i did. hopefully that i helpful. good luck!