Nah, I don't agree. Ramón would have killed her himself; they wouldn't have left any witnesses behind anyway and on the top of that she was a very intelligent and dangerous woman, that would know how to get revenge on them if left alive. He was probably just slightly pissed off at Esteban 'cause he killed her so soon while he wanted to enjoy her suffering for a little longer.
I think it is somewhat ambiguous, and intended that way. Ramon gives Esteban a sort of strange look, slightly puzzled. I think it is meant precisely for that reason; you are supposed to wonder: would Ramon have actually done that himself? Can't be totally sure, but maybe not. I believe Frayling said a similar thing on the dvd commentary...