***Also, one of the more challenging things about singing the role of Amalia is the song "Where's My Shoe?".****
I was just about to make the same comment. i would say that's the only really challenging song in the score, in itself. An isolated high note like the one in "Vanilla Ice Cream," even a B-flat, should not in itself be difficult for a soprano to sing unless she doesn't really have that note in her range to begin with :-)
Julie Andrews has said that Eliza was an extremely challenging role to sing because the performer has to go from guttural shouting and screaming in some of the dialogue to singing in her lower, almost belt register for some sections of the score and then pretty high into the soprano stratosphere for other sections, all in the course of three hours. Except for "Where's My Shoe?", the role of Amalia is not written in the same way.