glad you took those steps. I am not sure about the KLX and electric start if that is a concern for your wife. each of the 4 strokes are easy to start if the carburetor is close to clean. Ditto with the kx100 if you keep the carburetor clean and a clean spark plug. I have had one in the family and other one that might as well have been in the family that we set up for a 'senior rider' who is over 6 feet. if you are considering the kx 100 dont pass up a deal on a kx85 either. the cylinders swap in about an an hour, and other than shorter wheels (something that a shorter person my be fine with anyway, at nearly 6 feet i ride the small wheels as well as the bigger ones).
I would just let what you can find deals on clean ones decide that one. if your wife is as athletic as you say she wont have any trouble picking up either with one hand (seriously, she just needs to know the technique as in any other lift). fyi the smaller wheel bikes are also easier to rock back up for a small person. fyi the kx 85 is also a little faster than a kx 100 due to the way kawasaki chose to concentrate the power towards the lower end on the kx 100. once you put the kx100 cylinder on the kx85 you have one of the easiest to ride bikes on the planet and it weighs less than the kx 100 by about 8 lbs when we weighed them years ago (pre power valve engines).
the yzf and the crf do not have e buttons. they also have close ratio racing type transmissions, though both can be converted or geared down until you get some trail skills. the problem with each of those is they are not good go slow trail ride rigs. where you may not really need one to be like that, you will find yourself happier at a much higher speed than someone on a beginner bike will be. conversely you won't be as happy going slow and riding with those on slow bikes. you end up waiting and the other person ends up riding alone. so if the idea of riding together is part of the attraction, chalk one up in the loss column. The crfx and the wr will make you more easily able to match your wife's speed and make the ride more fun. I suggest people buy bikes that work well together if they are going to be riding together. I dont think you can even guess how that will play out from where you sit now. I have several bikes and I have always had one to ride when I go with the beginners. more for me than for them.
Whoever is telling you about the reliability factor between the crfx/crf and the wr/yzf has given you some very questionable advice. To be honest, it is just plain not the case as the percentages play out. The WR when treated the same as the crfx is the hands down winner when it comes to reliability. I am more pro honda that probably anyone you will find on this forum and MANY other ones (I own lots of hondas including a crf that has a crfx transmission installed). The WR lacks a little bit of finesse and polish as oposed to the honda, but it is the more trouble free, starting at the head (valve issues on the honda can be fixed for around 1200 if you are getting it all done at a shop), and then move to the transmission. I would not be scared off the honda by the reliability (always avoid the 2004 crf/crfx because in addition to the head/valves they have a cylinder issue), but you probably won't be as willing as I am to deal with those issues.
anyway, don't be too shy about getting a wr450 either. it is a nice slow go bike and can still keep you hp happy for the rest of your life.