Muger?

I just read Georgette Heyer's The Spanish Bride, which worked well enough as a military narrative. Heyer's use of Spanish bothered me, mostly because it seemed inconsistent with what she told me (as a reader) about Juana and Harry Smith's daily life. This is one of my pet peeves in books and in movies. If the audience is made aware of the other language but the text remains in English, please be thoughtful about how that other language is conveyed. Scattering Spanish phrases in with English dialogue when you've told me already that they are always speaking Spanish feels fake, forced and awkward to me.

Orthographically speaking, how long has mujer been mujer? Was it muger in the 19th century? Heyer spelled it that way several times in the book, and now I must go find out the history of the spelling and pronunciation of the word.