A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,421
To be blunt: Your flying TATL to bring an underage girl on an international flight could look like trafficking. If she doesn't have her parents' consent to make the trip, both of you could be in trouble but you much more than her. In some jurisdictions, there could be a presumption of statutory rape since she might be below the age of consent (in some but certainly not all places in the USA) while you are considered to be an adult.
She can fly without an adult at 17, but she probably needs some particular form of documented parental consent to check in and cross borders at 17. Do her parents really approve of their seventeen-year-old daughter visiting an older guy in another country for several months? Does she have sufficient maturity for this? Would she miss several months of school? What about your school or work? There are also issues such as medical power of attorney (since minors cannot make most medical decisions, including in emergencies). BTW, I hope you've thought about medical insurance for the trip.
Also BTW, how did you meet and how well do you know each other? If you've only "met" online, please think a million times before proceding with this.