I don't think that there would have been anything stopping her completing her GFT on her 16th. Birthday and then fulfilling the solo including the solo QXC requirements. A very long day indeed if she wanted to apply for her licence at the end of it, but the GFT could have been conducted at any time during the day and it would have only lasted about an hour - less if the examiner was one of her instructors who was already satisfied as to her standard.
P.P.