Shelley is a Cloudcuckoolander because of the events told in the Zombie Story Arc.The Shelley in Bobbins was relatively sane. Then, early in SGR, she got killed and buried, and probably already started to decay when she was zombified. Then she got de-zombified and revived by a lightning strike. It is reasonable that something like this affects the brain permanently. Luckily she is still able to function as a productive and indeed quite resourceful member of society.
Shelley is an immortal of type IV.She can be strangled or shot and will be clinically dead afterwards - but SOMEHOW she rises again. At other times, when in lethal situations, she averts death altogether in rather improbable ways. It is af if Destiny itself doesn't allow her to die for good.
Shelley is technically still a zombie.Albeit a zombie with healthy skin, good manners and an excellent modern fashion sense. Still her worst fear seems to be her inner zombie. Also her clone is a zombie. in walking distance of Wakefield, a real city in West Yorkshire. And just a few kilometres south-west of Wakefield, there is a village named... Shelley!!