In her defense, from what I understand, the film version of the book really tones down the lesbian relationship between Celie and Shug. If before auditioning for the show and accepting the role of Celie she had only say, seen the movie and listened to a few songs from the OBC, it's entirely plausible that she didn't realize Celie is queer/bi/lesbian. She certainly wouldn't be the first actor to accept a role with only that level of knowledge of the show.
Something I've been thinking a lot about recently is the fact that everyone - both liberal and conservative - are products of their upbringing and their community. There are a lot of fundamentalist Christians out there who (idiotically) think homosexuality is a sin. If the majority of a child's family, friends, and acquaintances believe this, then the child will be almost inevitably led to believe it too. Although many theater people from conservative backgrounds end up becoming more liberal because of the new friends and colleagues they make as adults in the performing arts, some still manage to stay in their conservative "bubble" and are never properly challenged to think a new way.
She really should never have sued the producers over this. I'm sure her family, friends, and fellow members of her church encouraged her, and that she simply does not know enough gay people to have any realistic perspective on homosexuality. And although I can understand her not reading the entirety of the script to the musical when accepting the role, the fact that she only recently read it (after what, a year?), and has not only admitted this but is using it as part of her case...what a sad, pathetic person. I hope she likes singing in church because she ain't going to be singing in the professional theatre - and that's a choice she has consciously made. You can't be openly anti-gay and be a theatre professional - not outside of say, Utah and South Carolina. I just hope she doesn't actually get any money out of this idiocy.