Get a TT-R125LE, or some equally small bike with electric start.
Sorry, a 125 two-stroke is about the worst possible choice you could make and it virtually guarantees your wife will never, EVER go riding. In fact, ANY MX bike is a bad choice.
A KDX200 is an equally bad choice because it is relatively tall and heavy.
You want small, light, and electric start for this application. Why? For one, she'll be WAY more confident if she can flat-foot the bike (see trailqueen's comments above). If she's not confident, this isn't fun. Along the same lines, the surest way to turn her off on riding is to put her on some big, heavy pig that she can't hold up when she stops in a bad spot. Her getting pinned under the bike when it falls over not only exposes her to potential burn injuries but it is also sure to sour her on riding. You also want that E-start because kick-starting the bike for the 15th time after she stalls it, yet again, is yet another way to take the fun out of it. Remember, she's not into riding like you or I, so if it isn't fun right off the bat she's not going to keep plugging away at it, she'll just quit.
Yes, if she takes to riding then more than likely the TT-R will be outgrown fairly quickly. Don't fall for the idea of getting something she'll "grow into" because that will be too much machine for her to learn on at first. Yes, it will cost you a bit more money this way. Would you rather have the extra money or would you rather have your wife interested in riding with you? Hint: the latter makes future bike-related purchases a LOT easier.