Bathing can be problematic because there are multiple strange things going on that most dogs aren't really familiar with.
First the location. Bathtubs and shower stalls are often made of a curved surface that has a single color. This is hard to see for dogs, so they might stumble, freeze or want to jump out. Putting an old towel that has a contrasting color onto the bottom of the shower can help.
Next: the sounds. Being enclosed in a shower stall or even just in the bottom of a bathtub changes the acoustic dramatically. Add to that the loud noises dog nails make on the surface of the bathtub. That can be pretty scary for a dog. If possible, I would keep the shower doors open. In addition, talk to your dog in a calm, quiet voice. Tell her everything you do, just to keep the chatter up.
The water. We humans are used to showers, but when a dog gets wet, it's usually either out in the rain or walking into a body of water. To emulate this, you should start wetting your dog from the bottom: first only the feet, then the legs, then the chest. If possible, keep the top of the shoulders and back dry. That's where most dogs get anxious.
Keep the face and head dry at all times to prevent ear infections. If there is dirt in the face, wipe it off with a soft, dry brush or with a damp (not dripping!) wash cloth.
The drying: don't throw a towel over your dogs head to dry her. Instead, kneel down and offer the towel like you would offer a hug. If she comes to you, make toweling a fun activity where your dog is allowed to play like she plays in the mud.
