Tom-
I second the riding course. I found out very quickly that I don't have what it takes to teach someone how to ride a motorcycle. My wife liked the class and the fact that our instructor was a woman helped put her at ease. (She really wanted to learn how to ride, but was really scared at first) I personally recommend the Harley course. You can argue it's part of their marketing arm, but it's 2 days of classroom instruction and 2 days of on-bike practice and it's geared for those who have never sat on a bike before. Plus, they keep you in small groups of 6 so there is more time for one-on-one instruction if anyone needs it and you are on new (or fairly new) Buell Blasts. It's a 500cc thumper which shakes like any good Harley product
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The local community college courses run by the state (in Michigan) are only $25, but they are large groups and they teach you on beat-up bikes. Also, they are only a couple days, so unless you learn fast or already have bike experience it will likely be intimidating for someone who's never ridden before.
One other piece of advice that Linda (Smithrelo on this board) gave me is that when you two ride together, let her lead. If she follows behind you all the time, she'll get used to watching you rather than looking around for road hazards. If she's leading that will give her practice keeping her eyes moving.
As for bikes, when you're looking around have her involved with the process. Have her sit on the prospective bike and see if it's comfortable for her. My wife is only an inch taller that yours. We first looked at the Honda Rebel (CMX250) and while it's a nice, cheap little bike we felt we could do better used. Rebels are hard to find used as a lot of folks seems too attached to them to let them go after getting another bigger bike. We found a mint Honda CB360T and it fit the bill. It's light and easy to handle and she could practically put her feet flat on the ground with no modification. I found a shaved seat for it on eBay (as the original seat had a few small tears in it) and it was perfect. She cut her teeth with it for a summer and she got more and more sure of herself riding. I had to go easy with my 750, but once she learned it was OK to let it wind up it could zip right along. The only issue with the 360 is that all the power lives up at high RPM. Plus, despite being a Honda, the 360 is a prallel twin, so it still vibrates a bit and after a long trip, her hands would be almost numb.
This year, time to upgrade. She wanted a 4 cylinder for it's smoooooth running quality and with the 750/4 being too heavy and a 350/4 being scarce the 500/550 seemed like the way to go. I located one from a board member (chemmy) and she loves it. Although a bigger bike, she finds it easier to ride and finds it a better balanced motorcycle. It's a bit tall for her and when stopped she's on her tiptoes. I need to get the seat cut down a bit (It has a few tears that need repairing anyway) but the only real issue with her being on her toes is wrangling the bike around to park it. But, the 550 has more lowering options than the 360.
So, that's the story of what we went through. Hope it lends you some insight. Good luck!