Bubba is a 22 year old, shy-looking girl who is a neighbour to Olive's house. Ever since the age of five, she has regularly associated with Roo and Barney everytime they had their lay-off season and came back to town. It is because of her that the tradition of bringing back a doll was started.
Although she seems shy on the outside, she is not as innocent as her appearance would have seemed, because she knows about what Roo and Barney do every time they come back, i.e. Recreational sex. This is demonstrated by the dialogue between her and Pearl at the beginning of the play "Bubba: You won't need any (books) till after April." By that line she means that Pearl would most likely be too tied up in having fun with Barney to be reading books. Pearl is surprised by her knowledge of sex, and talks to Olive, saying "Pearl: Yeah.
I'd say she knows more than her prayers." This is an euphemism of meaning that Bubba knows about sex. Despite that, Olive obviously still treats Bubba as an immature, prepubescent child that she was when Roo and Barney first came. "Olive: Bubba? Don't be silly, she's only a baby." The human condition of portraying Bubba as a naive child came up again later when Olive said that "Roo and Barney she treats as if the were uncles."
Even though Bubba knows about sex, and from this it can be concluded that she is probably no stranger to light relationships with the opposite sex, she is still emotionally not yet an adult. The human condition of Bubba mentally is shown in this quote, when Bubba says "Roo, why didn't he come down (Barney)? Four letters we wrote him," questioning Barney's motives and his emotional workings. This quote...