I regret to inform you that it is another ex-wife.
The funny thing about this lady is that she is voiced by Nancy Cartwright - they tend to avoid using Nancy for incidental side-women as the show goes on, but occasionally you'll catch a fully-grown woman like this who sounds suspiciously like Bart. We have certainly encountered this Bart-esque phenomenon before, and I think I'll notice it every time. It's almost as rare as a Yeardley Smith voice.
The shot that follows the ex-wives exchange is one that made my blood run cold:

Listen, I love you guys, but we are NOT covering all of these people individually.
This post is part of my "Every Simpsons Character Ever" series. For a list of my rules in this project, click here.