Hey L., my name is Jenn and I've been in Nursing for @ 10 years. I've cared for from little people ( 10 minutes old ) to big people ( 102 years old ), so I consider myself a bit of an expert, so I'll tell you what I know.
Some children have "EXTRA" sensative perceptions, especially to touch. I'm curious to know what time of day do you bathe the baby...depending the time DOES make a difference. Preferably a nighttime bath, you can use the lavender baby wash, it will induce IMEDIATE sleep. Try taking the baby in the shower with you to show her that it's "okay" because mommy's in the shower too and your body will be up against the baby. So she will feel secure. Babies at her age still have a bit of a time with their physical boundaries. so this closeness and arm wrapping will help secure her even more. Introduce her feet to the water first, let her kick around, talk soothingly to her, "Isn't it nice", you'll be able to tell when she starts to feel a bit comfortable, then introduce her hands, legs, etc.. If this truly doesn't work then I would take her to see her pediatrician..this could mean she may have a sensory issue. I'm not a 'licensed' individual, but I do have a lot of experience...I hope it works!
Jenn.