<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by awm:
Passport number, Passport expiry date, date of birth and booking res. number. And seat preference 
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If she is a US citizen, I think they have to ask you for a contact number & name in case of emergency, but I am fairly sure you can just refuse to give one. (It's the asking by the airline that is mandatory, not the reply by passenger)