Climbing the Duomo in Florence

I found this link to be quite helpful in deciding whether to purchase this pass or the Giotto Pass (we went with the latter):
https://eternalarrival.com/climbing-florence-duomo-brunelleschi-dome/

I had been ill for a couple of days leading up to the last time I climbed it, and had to turn around and go back down without making it to the top. An unfortunate way of knowing it is an option:). This was 20+ years ago, but I would imagine it’s the same.

I am terribly afraid of heights and I made it with some butterflies in my stomach. I was walking next to a guy who was even more scared than I was, but he made it too.

This YouTube video does a very comprehensive overview of climbing the Duomo and Bell Tower. It's long but you can skip to the Duomo section. Maybe it will help her decide.
https://youtu.be/QdbT0I4G6ds?si=pq8DySw2QBwl9AQs

The viewing area for the frescos is pretty close to the top, so she probably shouldn't try it. From what I remember, the opportunity to see the frescos up close happens on the way down, after you reach the top (exterior) viewing platform. It's a one-way process, you go up, then down, they don't allow you to go backwards (the stairs are very very narrow and won't fit two-way traffic). If I remember correctly, on the way up, there is only one opportunity to exit. I do remember seeing a few people who were feeling claustrophobic and/or afraid of heights who ended up exiting. The view of Florence and the hills are incredible, so you should definitely go.

If afraid of heights, I think the viewing of the frescos would probably be a bit more triggering than the top. It's very narrow walking around the dome to view the frescos with a plastic see thru wall where you can look up or down at the tiny people below in the church. Part of the frescos are viewed on the way up and part on the way down. There was someone in that area asking folks if they were feeling okay. At least at the top, you can step a bit away from the edge.