She's interesting in terms of the Doctor's psyche by this point. We can learn through Amy the Eleventh Doctor's motivations. In contrast to the other doctor's motivations, Nine's peace at all costs but no sacrifices and Ten's the order will be kept by any means necessary up to including sacrificing everything else, Eleven's main motivation seems to be keeping Amy and Rory alive at all costs, universe be damned.
This gives us a very valuable insight:
The Ninth behaved as he did because he had just emerged from the horrors of the timewar where he had personally condemmed two races to extinction and caused countless other tragedies through ripple effects. He appears to be suffering from a form of PTSD and will not let anyone else get hurt ifhe can help it, he also sues for peace every chance he gets. The one person he kills (that I can remember) is Cassandra and he does it as a cool headed judgement for her crimes.
The Tenth behaved as if he had become a bit more jaded. The order was kept by any means necessary and he behaves a bit more like a time travelling vigilante. As he says he sees things that will be, things that might be and things that must not be. He considers this his personal duty and woe betide anyone who runs counter to this. I actually lost count of how many times he carried out judgement.
The Eleventh, however, ...the impression I personally get from him is that he is old, he's spent his life fighting and now he's almost ready to die. He almost seems to display the thought "Why can't I have nice things?". As Ten he has lost many friends and done some terrible things and he is tired. Along comes Amy, this girl who believes in him though he constantly let her down who sees things he takes for granted, and he seems to resolve to himself that his duty is to protect her and those she loves. I think another lost companion might actually break his spirit. Most of the episodes seem to revolve around one of them dying (9 times out of 10 it's Rory) and the Doctor going "Oh, hell no" and going to extreme lengths to bring them back.
That's what we learn from Amy.
Unfortunately her arc is at a close, loathe as I am to say goodbye to two such good looking people (Amy and Rory) who drew attention away from some of the poorer episodes.