We went through this with my son at 2 and just recently at 3 1/2. For us it seems to be a sensory issue. If we make him, he becomes completely disregulated and starts to self harm and scream like crazy. It's heart breaking so we don't force it. The first time it happened we had to scaffold by starting as close to the bathroom as tolerable with a pan of water. After about a week he would stand by the tub and by 2 weeks he was back in.
This last time we were able to entice him with a exciting toy. We told him he could only play with the toy in the bathroom or bathtub. It took him 4 days and he threw some nasty tantrums but eventually gave in.
I'm sorry. I know firsthand how frustrating this situation is. Like your granddaughter my son loves the water in every other situation.

Yep. In earlier days, Luke and Kate used to love pools. Now, nothing doing. Thankfully, they still enjoy shower time.

Thanks. We will try this.

My son went through the same for a period of time. We had to force bath him which was extremely difficult. Try filling the tub with a little water and add bubbles or favorite water safe toys. Let her play and feel comfortable first. Wet hair gently with your hands. Allow her to try and wash her body. Do everything in a gentle manner. Almost like bathing a newborn. She has to ease back into the bathing routine. My son eventually went back to normal bathing. Hopefully she will to.

My son went through it as well, but it was related to a traumatic experience. Let me explain. He had never had a diaper rash as a child but one time he got very sick when he was about 3 years old. Along with the sickness came diarrhea. Even though I was quick to change his diapers immediately after a bowl movement it wasn't enough and the acid in his poop gave him a horrible diaper rash. My immediate response was to put him into a lukewarm tub to help soothe the pain - boy was I wrong! He screamed, I guess it made it WORSE. I eventually took him to the E.R. because he wouldn't drink anything and I was worried he was getting too sick. I let the doctor know about the bad rash and he gave me the most amazing ointment ever which cleared up the open sores within hours!

BUT.... that one mistake I made, he refused to bathe for around 6 months. I'd sponge bathe him every day, which he was fine with. It wasn't until a neighbor babysat him and was giving her own two children a bath (1 & 2) and she showed him how much fun they were having, that he was willing to get into a bathtub. Granted he STOOD the entire time, but it was a start. About a month later I was able to give him a bath once again.

So, is it possible something traumatic happened to scare her? Too hot/cold one time, or getting soap or water into her ears or eyes, or falling?Something that would make her think the bath was dangerous?

I'd try, if you have any grandchildren her age available, to see if you cannot get her into the bath as a "fun" play date.Because that worked for my boy.