Myrtle Simmons is Madea's daughter-in-law who makes her first appearance in the play, Diary of a Mad Black Woman.
In the play, Myrtle is the middle-aged widow of Madea's son who passed. She is the mother of Helen and Jackie.
In the movie, Myrtle is still Helen's mother, but is significantly older, being in her seventies. This is supported by her stating she had Helen at thirty-nine, as Helen herself is in her mid to late thirties(was married for nineteen years). As Madea is also in her seventies, it could only be assumed that Myrtle married a younger man(Madea's son), though, it could be possible that the age difference could be a little over a decade, as Madea could've had William somewhere in her early-mid teens way before Cora.
Myrtle first appears in Diary of a Mad Black Woman living in a home that Helen put her in. She tends to offer her daughter wisdom on her life and how to repair the broken pieces caused by her husband. Unlike the play series, she reappears in the sequel film, Family Reunion, and gives a speech to the younger generation about taking their place in society. It is also revealed that she and her husband had a great marriage.k