Heh, i liked the little stab at all Donna-haters out there with Donna's "I'm gonna travel with the doctor for a loooong time" quip to Martha.
By the way Donna has grow to be my favorite companion of the "new" Dr Who series, as she actually is able to solve problems, and find clues on her own, not just tag along and help by following the Doctors directions.
As for Jenny not changing appearance after the "regeneration". The Doctor regrew his hand in the X-mas invasion story, claiming it was withing 23 hours of the regeneration process... (some set amount of time anyway). Now maybe the same is true of a time lordy-being for the same amount of hours after birth / creation? That would explain why she didn't change appearance as she didn't regenerate, just healed an otherwise lethal injury while the body was still "freshly made".