Is negative G capability really of a requirement for something like a Spitfire?
Air combat is definitely not my specialist subject, but courtesy of Wikipedia, I believe the injected 109s could stick their nose down and bunt into a dive. When the Spitfire tried to follow, its engine cut out.
As I understand it, Miss Shilling's orifice was a plate with a hole that more or less kept the fuel where it was supposed to be in negative G.