I'm 5'1" and a smidge (that's an important smidge, too) and I felt really uncomfortable sitting so high up on my bike at first. I tried riding it while being able to put my feet flat on the ground when I came to a stop but it was incredibly uncomfortable after a short ride. Hills are harder to ride. Your knees start sounding like you're crushing a bag of chips. It's not happy.
I think it's a great idea to try her out on an Electra Townie. She'll probably overcome her worry over her balancing if she realizes that she can plant both feet on the ground at anytime. And they make some really nice looking bikes. Hello pink flowers! And matching basket -- good times.