Translating it to "our mother" is a fine assumption to make given the circumstances but little things like that can definitely come back later if, like this, she ends up not actually being her mother. Though if the queen did sort of welcome her into the fold, she could be considered her mother.
Probably would have been better not even to add the "our" in there, since even in English we will often not bother including those qualifiers if we're talking to our own family or people who already understand our family relationships.