it might well have been for the best that Meiling sunk her own chances at onee-san employment. Sakuya would not have agreed to it and you can't forget to ask her for consent on anything to do with Meiling.
Hmm, this has a similar premise to Fuuzen Lamp's short story, Shoukei no Ori, which also explores dragons and dragon turtles. Pretty much, Yacchie mistaking Meiling for her lost sister. Good read too.
Also, Meiling is a sleeping dragon. Because Gensokyo is so safe (everyone knows each other and people basically never die), Meiling never truly needs to wake up and reveal the extent of her talents.