Re: Flying with a guitar?
If you are flying Ryanair, Easyjet, or another of those budget airlines, I would recommend you pay the money to ship it and insure it.
In general, your girlfriend can attempt to carry it on, but her success will depend on how much room there is in the overhead bins. On many aircraft, the cased guitar will fit in the overhead, but if the flight is crowded, the attendants will make you check it.
If you have a good hard case, it ought to be alright, but of course there's no guarantee. I have carried on a full-size dreadnought case successfully and I have also checked a cased dreadnought with no problems. But other folks I have heard from have suffered damage to their guitars after checking them.