I had a sgt who was off sick TFN and made it too difficult to operate with his post unfilled. He was eventually posted non-effective to Innsworth although I believe he continued to remain off-sick at home.
Basically you are either holding a post or you aren't. As the OPs post obviously needed to be filled she had to be moved. As no one want to accept someone who will be non-effective then she would have been posted as non-effective. It sounds like she has been left at her original unit and is indeed open to a posting elsewhere when she becomes fit.