English technically has no third person gender-neutral pronoun. "They" is not "proper" English, though it is common usage these days. You'd still get points off on the GED test (I was a GED tutor for a while) for using "they," and a high school English teacher would still get out that red pen if you used it on a paper. "His or her" and "his/her" are also improper English, though overly-PC sources use it to try to avoid offending people and official documentation uses it to avoid any confusion.

In English, the grammatically correct way to handle gender-neutral pronouns is to pick one, either male or female, and then be consistent with it. So, if they used "her" in one line to refer to your singular retainer and used "he" on another line of the same dialog, that would be improper English due to the inconsistency.

Even though the vast majority of English-speaking people use "he" as the gender-neutral pronoun, "she" is just as valid, and the overuse of "he" in video games and technical fields is a lingering sign of sexism in English-speaking cultures. Of course, referring to servants generically using female pronouns isn't exactly a step forward. :P