I am currently reading a short Japanese novel targeted at learners of intermediate levels, entitled 野菊の墓. In this novel, multiple times a character is named only by お増{ます}。Based on the below examples I believe that this designates a specific character, probably the family servant/maid but looking for it in either the jisho dictionary or the goo dictionary did not yield more results that the typical "increase, multiply" sense of 増す。
Examples (taken verbatim):
ぼくの家には、母とぼく、兄と兄の妻、家の仕事をするお増{ます}~
ぼくはかばんを一つ持って、民子{たみこ}とお増{ます}と一緒に舟の乗り場へ行った。
きっと兄の妻やお増{ます}は、母やぼくたちがいないところで~
Is my understanding correct? What is the exact sense of お増? Is it a common word? Is it associated with a particular politeness level and/or era?