Well, if it's been 40 years and 50 lbs. since you've been on a horse, I'm guessing that your wife is older and perhaps has gained some weight, too (60+ years old?). If so, it's not going to be all that easy for her to restart and make this infatuation, real. I fully agree with Seahawk in that she should first take lessons. AND, she should get very proficient and comfortable before she rents a horse (and then should take 5-10 lessons on that rental horse before she goes solo so she and the horse understand each other fairly well).
My Palomino Quarter Horse is incredibly strong, stubborn, and smart and those qualities made it both fun and a PITA to ride him. To take advantage of and soften those same qualities, I would need to ride him five days a week, which I loved, really. But, if I could only ride him once or twice in a week, he would turn into a beast that needed quite a bit of tiring before I rode him. He might not be the "normal" horse, but horses can all of a sudden act up and guess who is going to pay the price?
He literally was my best friend for years upon years, though, so that is the wonderful side of owning a horse. With that said, a horse is essentially your child and needs to be taken care of and loved like one. It requires a lot of time, energy, and financial resources with the cost of boarding, shoeing, supplements, vet visits, etc.
Your wife should fully vet her experience with lessons and a horse rental before plunging head first into the reality of owning (and enjoying) a horse. With that said, owning a horse is truly a life style. Just like a child, it will change your life and will take the requisite time and requisite resources. Unless willing to make that commitment, limit the experience to trail rides on rental horses.
