Hate to tell you, but if bigamy is illegal, as it is in Texas (Penal Code Chapter 25.01), then it's not exactly a leap across the Grand Canyon to say that polygamy would be considered illegal too.
And these were not consenting adults participating, the "mistresses" in these cases were still considered children in the state of Texas. From what I understand, Mormons follow both the Bible and the Book of Mormon, so "render unto Caesar what is Caesar's and unto God what is God's". Did Jesus not advocate following the law as well? And last I checked, even Indecency with a Child was illegal.
As was mentioned in another thread, did you consider the fact that authorities may be protecting the potential reporting party? Maybe the possibility exists that, if they release her identity, she will be harassed by these cult members and their sympathizers and her testimony be subject to improper influence?
But of course, in your opinion, she's subject to her "master" or "benefactor" so her opinion doesn't really count because she's female. Who's discriminating now?