Hello, this is Dr. Linda. I hope I can help with your situation today.
My first impressions based on your brief description is she either has a joint infection, or has indeed sustained some injury to the area. This might be a soft tissue injury, possibly from a strain, or even a small fracture in one of the multiple small bones that make up the hock joint.
Because of her pregnancy, you almost have to consider having her checked by your veterinarian. He can first check to see if she indeed pregnant as this will dictate what medications can be used, if necessary. I would imagine that after a through examination of the leg & hoof, he/she will recommend taping the fluid &/or proceeding with radiographs of the area.
You are pretty limited with your choice of drugs, both antibiotics & anti-inflammatories at this stage, so I definitely would not recommend you doing any more than your DMSO. But if she is a show caliber animal, then you really want to find out what is going on just in case the problem in the hock progresses to a point where she can no longer walk, & you lose the potential for obtaining future calves from her.
I hope this makes sense & you find the information helpful. Please let me know if you have any further questions or concerns.