The measurement for selecting the right frame recumbent bike or trike if there is more than one frame size is called the "X seam measurement". If you want to compare two people to see if their X seam measurement is close, look at this YouTube video. That will give you an exact idea of how different you and your wife are. If you are not within a few inches, the trike will not be set up for your comfort.
How To Measure X-Seam