AP helps improvisation (mostly keyboard and strings, less so brass, and even less so woodwinds, I can explain later). Also, ease/speed of composition, allowing you to focus on the creative aspect of composing, or just simply composing more.
You can become a great improviser with relative pitch, but it is much harder, as you have to calculate the intervals between notes in real time, whereas AP spits out the exact note automatically for you.
You should ask your daughter if she would be interested in Jazz improvisation! That is where her AP would actually shine. We need another Stephane Grappelli! :D
I am a violinist myself, and although I can play every scale and arpeggio in the books, I still can't play freely what I hear in my head vs my fingers even after years of working on my real time relative pitch.