My name is XXXXX XXXXX X am a Vet tech for 30+ years. CVT_in_MN is not on, so I will be happy to address this problem with Molly.
What you are describing may be a spinal issue called IVDD. This is similiar to a human getting a herniated or bulging disc in the spine. Molly should be examined by a Veterinary Neurologist who can do a complete Neurological Exam. They may decide to do a CT, MRI or Myleogram to see what is happening with the discs. This is some information on IVDD(Invertbratal Disc Disease) which is a possibility: http://sevneurology.com/articles/intervertebral-disk-disease-ivdd-in-dogs .
Active dogs can twist wrong and injure the spine area and some breeds are more susceptible to this problem than others. The longer bodied short legged dogs like the Doxie or Corgie are prone to IVDD, but Spine injuries can affect any breed. The Steroid injection is the first treatment usually done with this type of problem. What is usually suggested after the initial injection, we recommend complete kennel or crate rest. If she has to go out, be cautious with the towel lift and support her to go potty and get her back inside for more rest. This is very important to help with the reduction of swelling and to help Molly feel better. To find out what the next steps for treatment should be, I would get an appointment and have her see a Veterinary Neurologist to see what further protocol they recommend. Steroids long term are very hard on dogs. If she is having pain, they can decide what type of medications would be best to help her. To find a Veterinary Neurologist you can use this link: http://www.acvim.org/PetOwners/FindaSpecialist.aspx put Neurology and your State in the blanks and it will bring up a list to help you find a Neurologist. You can also speak with your Vet about a referral.