I can't tell who got to her: Cersei or Tywin. Her statements sound like Cersei's words, frankly. Blunt, unsubtle, and direct. Damning, to be sure, but sounding more like the words of a puppet than genuine testimony.
What I can't tell, however, is Shae's motivation. On the one hand, the books (as I recall) made it sound like the results of a woman scorned. On the other, I wonder if leverage was applied to her, convincing her that if she said what she'd said, Tyrion would be spared to take the black. On the show...with Sibel Kekhili's acting, it was far more ambiguous (which I think is a testament to her astoundingly good acting chops). Anyone recall how it plays in the books? I mean, without spoiling where that particular storyline goes, or at least warning folks before posting.