If she is 5'5.5" then you should give her a 16" frame i.e. middle of bb to top of the seat post. She looks like she is more than 5'5.5" in the pics.
The clearance on the top tube from the pics are not that good to be frank and even with a loafer shoes standing she just, only just, managed to clear the top tube.
Think of it this way when you fall/dismount etc you will normally fall onto the middle of the top tube and not right in front of the saddle where the slop is the steepest that provide the maximum clearance. (happened to me a few times in the middle of the top tube and it was painful … )
Nice frame btw but 16" will suits her better.
🙂