Tho I prefer her name with the 'z', I do remember in one of those interviews Claremont said that the correct spelling is 'Elisabeth' with the 's'. Guess It got retconned or Marvel just prefer Elizabeth.
I don't see it as a retcon, just adding more layer background to her childhood/teenage days. Betsy in her Marvel UK days started out as a young woman probably around 18-19 yo (Brian is in college and she's the same age as him).
Her childhood days were never fully explored until Claremont add it in the body shoppe memories.
She could still be a tomboy during her childhood days, but she also might be getting more feminine after she reached adolescence not to mention after getting to know modelling