The other thing, be sure to have her take the MSF contemporaneously (or after) the butt testing. The first time I tried the blast, I thought that the regular seat was too high, but it was because I didn’t know how to relax into the the seat. Not really afraid of the bike, just not comfortable on it. After I took the class, it was a whole different story.
I’m not much taller than your lady, and I was really surprised to discover that most of the bikes that are listed as “beginner bikes” actually fit me pretty well from the flat-foot point of view.