I’ve checked the Spanish opening credits of Abre tu fosa, amigo … llega Sábata: they mention only two actresses, Havana-born Tania Alvarado and Irene D’Astrea, who plays the “posadera.” IMDb credits Fanny Grey with the part of the “chica rubia de la posada” – erroneously, as you, always right on such matters, have pointed out.
The credits of La diligencia de los condenados’s Italian version, Prima ti perdono … poi t’ammazzo, mention four actresses: Erika Blanc (opening credits), Elena Pironti, Maria Cinthia Rosello and Leontine May (closing credits). And here, poor fool, I stand once more, no wiser than I was before.
In this case you’d try a different direction: maybe in the '70s she was credited in some non-western movies from the same director or producer (Ignacio Iquino).
Just a quick info on the German BluRay which I am watching at the moment: there are English and German subtitles included, but only for parts missing from the respective dubs vs. the Spanish uncut print that was used. However, the missing parts are not identical, which becomes apparent when you activate the one subtitle, but the other dub (e.g. watch in English with German subs).
