Why (Spoilers)

No. She was speculating about the criminal profile of the second killer and, as the sheriff came to realize that he fit the profile, he admitted that he was the killer, attacked her and revealed his tats thus confirming he was the killer. If he had remained quiet and not attacked her, she would probably have rambled on without putting it all together. She wasn't the brightest. Married Jabba the Hut after all!

Apparently he intended to attack her anyway because, with her husband and his mentor dead, he felt free to carry out his sexually sadistic nature against her. Also, the deputy had earlier told her that the sheriff wouldn't be back until the morning. The sheriff came back at a time when he knew he would be alone with her.

She did figure it out. When the sheriff was talking he said something about being desperate and Miranda said desperate enough to talk to me. So she did figure it out.