Interesting! We have all three kids done with the "for" so I looked it up too. I'm not allowed to post URLS yet - but I did find that she can can sign herself and "for" is okay too according to travel.state.gov
I guess you can go either way. We signed out kid's first passports (they got them at age 2), but both learned to sign their names in cursive by kindergarten, so they signed their renewal passports at age 7.
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