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
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
Of course you can't find Tackleford on any map. But we know, that it is 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