I searched some more (what I should have done BEFORE I posted the story...) and discovered that Mrs is mostly written out as "Missis". I rely on:

http://dict.leo.org/ende?lp=ende&lan...ssis&relink=on

"Misses" is the (probably old-fashioned) plural form of "Miss".
I hope this will do it:

"My name is Rita Sullivan; Missis Sullivan."