In the play Ruth seems to play the role of mother figure to all characters. She acts as peacemaker during the various conflicts that go on between her family. She looks after Travis and does her best to bring him up. She speaks to Mama on behalf of her husband. Note how she tries to sooth Mama after her argument with her children:
RUTH (Soothingly, older than her years) Now.... you taking it all too serioiusly. You just got strong-willed children and it takes a strong woman like you to keep 'em in hand.
It is interesting that Ruth is described as "older than her years." It is clear that in this family she is the mature one that manages to hold all of the disparate elements together.
However, her role as mother figure is most cemented by the discovery that she is pregnant. Her decision to keep the baby is one of the key indicators that suggest hope for the Yonger family as they move to their new place and confirms Ruth's role as nurturer of the Younger family.