I always read it as her being incapable of believing she can rely on anyone, and therefore not letting herself do it. (And stubborn as a mule, of course. ^^) I think she can never assume that she's anyone's top priority, even if she might be able to convince herself that their intentions towards her are good. :/

Seanan's Tumblr is good fun, and a pretty incongruous mix of stuff. (I have resigned myself to the fact that following my favorite author means intermittent exposure to surprise!spider pictures. >.>)