Amy Pond has no characteristics > She doesn’t have a deep, deep fear of abandonment, a fear which leads her to push people away
(Sarcasm mode off, and possible trigger warning for child abuse/neglect)
Amy expects people to leave her, because that’s all they’ve ever done. (Her parents, remember?) So she says to Rory in disbelief, “We’re still together in ten years?”, she tells the Doctor “I understand, you’re got to leave me.” She hates being ‘clingy’- because everything she’s clung to she’s lost. She even makes fun of Rory for being ‘clingy’ when she was terrified too, and probably would have been even more so if their positions were reversed. When their roles are reversed in the worst way possible, and Rory is dead (er yes, this happened twice) she completely goes to pieces. She either folds in on herself and seems dead to the world, or she becomes utterly hysterical. (Remember?) Plus, her relief at not being abandoned to die in Flesh And Stone leads her to try and sleep with the Doctor, even though he protests, which is obviously not healthy behaviour at all.
But of course you can see where all this comes from. At this point in her story she’s never had a childhood with her parents, and Aunt Sharon doesn’t seem to have been the most attentive of carers. (She left 7-year-old Amy alone in the middle of the night! That can lead to prosecution, in Britain, and it’s just one of those things you just don’t do to a kid, no matter how mature they seem. What the hell, Aunt Sharon?) But once Amy gets her parents back and her childhood is restored, this behaviour lessened considerably. No more mocking people for being clingy, and she generally seems happier all round.
However, we still see Amy working through this fear- firstly in The Girl Who Waited, where she is accidentally abandoned and it turns her cold, hateful and hard. Then in The God Complex, Amy’s greatest fear is represented by herself sitting waiting- but it’s not waiting she fears, it’s waiting and no-one coming for her. True, a lot of that scene is about the Doctor, but it’s about Amy too. Lots of people’s worst fears spring from their childhood experiences- “I stole your childhood” -and Amy’s no different.
And of course, when Amy fears that Rory will abandon her for not being able to have children, she abandons him first. Luckily, she and her husband are able to talk it out, albeit in the most painful and stressful way imaginable. Anyway, there you have it. I think we know, beyond all shadow of a doubt, what Amy’s worst fear is.