Well, you could do like I do with Coconut and just bathe her outside. Coco is NOT a fan of the tub. Even the roll-in shower (I think she has slipped and fallen too many times). I literally have to tie her to the wall to keep her in there, and she will shake the whole time. That's just not healthy for either of us. But she doesn't mind standing outside on the landing and getting bathed with the hose (obviously doesn't work in winter). So I just tie her leash to the deck and do her out there.
Phoenix, once he realizes that he isn't getting out of whatever you're about to do with him, tends to fall asleep. So it's tricky keeping him on his feet during bathing lol. But I also use one of those bathing tethers, just to make sure he doesn't jump out. And I take him to the groomer every 2 or 3 months to get a really good scrub and trim and everything. And they've never reported any problems with bathing him (only blow drying him, but he's always been a brat about that).
If the dog is scared of the tub specifically, make sure you have a good mat in there so she doesn't slip (which is the cause of fear in a lot of dogs, such is my understanding). If it's the bathroom in general, don't take her in there ONLY for bath time. Go in there and train, play, just hang out. Maybe start feeding her in there. Anything to make being in the bathroom a positive thing.
Phoenix was a little nervous about my bathroom when I first brought him home, because it was new and very small. So I would take him in there with me and just let him snoop around while I did my thing. We'd go in there and I'd sit on the edge of the tub and do short training sessions with him. I'd put him in the empty tub to play. One time I had to clean something off his ears, but didn't want him getting wet, so I bundled him up in a bunch of towels and put him in the tub. He ended up taking a nap like that.
Coco will follow me in the bathroom because she knows she gets lovins. And she naps in the doorway when I'm home alone taking a shower. So long as she's not in the tub, she has no issues with the bathroom.