Yes, Tsunami 140 is too big for your wife. She is a couple of inches taller than me but still a small paddler, especially on weight. If you choose Small on WS’s own web site they will not list any Tsumanis for a small paddler.
You are not properly accounting for the fact that you really do not yet understand what fit should be for spending a long happy time traveling in a kayak. It is deck height (the 140 is IMO a bit high at 14"), overall volume to get to the right waterline (the max capacity for the Tsumani 140 is more than three times your wife’s weight), etc. And I don’t think you are seeing anything but length. In fact a 16 ft Tempest 165 is a better fit for her than the shorter Tsunami 140. Because of volume, deck height, width etc.
The fact that she was OK plugging along in a 17 ft boat that was likely too large for her in a first time out does not mean that she will be happy trying to keep up with you over longer trips in a boat is over volume for her. She will be tired and will be struggling to match your speed.
The long term result is that you become a solo paddler. I have seen this happen over and over when the guy jumps out and makes choices for the wife before they themselves understand what fit should be. If you want that result fine, but if you want a paddling companion take the time to go to Charles River or other places within a reasonable drive to get some proper help in fitting.