I love your, and some others’, analyses on TCoAaL. Now, about a week or 2 ago, I got the thought in my head that maybe Ashley’s portrayal could qualify her as, if not a manic pixie dream girl, a darker variant: a manic pixie nightmare girl. At least based on the info in the MPDG article on TVTropes. The neuroses and possible personality disorders wouldn’t be negated, of course. Could I have been onto something? Might I have been cooking, or was I just burning a cup of water?
TV Tropes is a viewer-oriented classification of devices or cliches, so the answer is that if you think you saw something, you did.
The manic pixie dream girl trope is an observation of a particular aesthetic implementation of what I will begrudgingly call 'the Call to Adventure' even if I think the idea of the monomyth is broadly full of shit. It's a (usually) flat (as in, static, no character arc) character type that acts as a force for change upon the protagonist and (usually male) his situation.
Given that, what you're looking for is... If you view Ashley as the force for change upon an Andrew-centred narrative and follow the thought all the way through, what does that have the story say? That's more or less how I'd apply the lens, anyway.
I don't generally like TV Tropes for analysis myself because it misuses academic terminology I will die mad about this orients itself from a generic crowd-sourced 'viewer' perspective which can be informative to read about but I don't generally find super useful to apply critically.