That's kinda strange. The process I'm familiar with, you get your student pilot license during training, then you get an endorsement from your instructor to solo. After you've had sufficient instructional and solo time, you take your practical test / check ride, and get your private license.

Maybe this was a requirement of the flight school rather than a licensing requirement? Maybe she got her private license in gliders or balloons, and wasn't yet qualified to solo a powered aircraft?