What was your response?
Why do you think she is or why did you ask her that?
How long have you been married?
How old are the two of you?
Many times when a person answers a question with a question it's out of guilt. However, it could be guilt of an affair or it could be that she thought it might upset you to know that she knew who's car it was considering what she told you three years ago.
The botXXXXX XXXXXne is the best indicator of future behavior is past behavior, so you have to ask yourself, has she been deceptive to you in the past? Has she ever cheated on you? Has she ever lied to you? If she has, then it is likely she may do it again, but if she's been upfront and honest with you, then I would suggest giving her the benefit of the doubt, unless you have more proof. I welcome your thoughts, let me know if you want to talk more