Things that I'd look for her..some mentioned...
Frame that she can climb aboard (lift leg over). Consider stopped and feet on the ground. Unless you customize a fuel tank.
Seat.. WalMart and other suppliers have a very comfortable seat. I have very little azz and need a good one for my bones.
Springer front end..much easier ride.
Handle bars, what ever is comfortable. I like the cruiser bars, detest apes. My .02
Consider dual brake lever.
My son and I built a bike for his wife of 4" 10" (she be mad if I didn't say 4' 10 1/2")
Here is another bike she can ride. This belongs to my oldest son. Also short and stocky.