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I am sorry to hear about the injury to your ferret. You really should take her to the vet as soon as possible. Your vet will be able to assess the trauma to the abdominal organs, spine, and most importantly the spinal cord, which directly affects the use of the back legs. There are medications that can be given to help reduce the swelling around the spinal cord, and in particular I suspect your ferret needs to be on some pain medications to make her as comfortable as possible.
Many times with spinal cord injury the timing of getting them treated properly is crucial to whether they will recover or if there will be permanent damage.
Good luck with your ferret - hopefully your veterinarian will be able to determine the extent of her injuries quickly.