I wouldn't say sand-bag, but she didn't press either previous fight nearly as much as she pressed Rousey. They literally look like different fighters. Now, whether that's due to it being a championship fight and adrenaline or something else, I have no idea. But stylistically the Rousey fight doesn't match up super well with the previous ones.
And honestly, I'm sure they were eyeing her for the Championship fight regardless, since she had quite a bit of non-mma hype behind her and Rousey had mopped up the rest of the division. Simply winning was all that was really necessary to get her to the big show, and her performance in those previous fights certainly didn't show how top-quality she theoretically was. She may have simply been trying to avoid getting hurt or dangerously caught because she knew she would be getting a title shot. But I don't really think that she kept her normal form intentionally before going super sayajin on Rousey.