As an avid reader of StackExchange she becomes a bit paranoid - what if she should lose this new form? She is concerned: should a Magical Dispelling strike, she would once again be that stupid, nasty, dirty little girl with those grimy-grubby wings... that happens to sing quite well.
She searches for, then finds, a portal into the Fell Shadows. Dragons which spend sufficient time there turn into Shadow Dragons (MM 84). Assuming success, she becomes one Shadow Dragon wyrmling well before her fifth birthday (that is to say she isn't a 'young' dragon yet).
"Aha!" she shrieks with delight, "Now I am genuinely a dragon... a DRAGON FOREVER!! Take THAT, Exchangers of Stack!" The cold hard rain falls as lightning cascades in the distance ominously. Indeed, has this mere harpy of a girl outwitted us?
Question: Does a transformation into an entirely different creature (such as changing types &/or transforming bodies) mean that Dispel Magic cannot undo a 'permanent' True Polymorph spell? Or does this apparently-totally-'new'-creature take this polymorphic-dispelability along with them?