It's possible that the injury your hen sustained caused damage to her tailbone or spinal cord, which could have resulted in the inability to lift her tail. This type of injury can sometimes lead to tail paralysis or a condition called "limber tail," where the tail droops or hangs limply.
In some cases, if the injury is not properly addressed, scar tissue can form and cause the tail to fuse in a certain position, which could explain why your hen's tail seems stuck in that position.
If your hen is experiencing pain when you try to lift her tail, it's best to avoid doing so as this could cause further discomfort or injury. I would recommend consulting with a veterinarian who has experience treating chickens and can perform a physical exam to assess the extent of the injury and recommend any necessary treatment or supportive care.