Big Brother and many other reality shows are entertainment shows. They are not game shows regulated by the FCC.
I think it has been apparent for years that the show is manipulated, but I don't think the producers always get what they want. For example, Helen allegedly said on the feeds that the diary room did not want her to nominate Howard last week. Last year, Shane said the diary room didn't want him to nominate Frank, but then he did anyway. They can suggest, but they don't control. Given that, I don't believe there is a "predetermined winner". Rather, I believe there are "production favorites" that they try to help via twists and diary room pressure. IF she is a friend of the producer's, she was probably just cast to create drama and be a big personality. I don't think it is anything more than that.