I don't think she really had all that horrible of a life. She was very privileged, yes, even if she was sheltered, and she grew up very quickly. She's capable of thinking for herself, even if her plans at first show her naivete. I don't think she's lost, as you put it, I think she's still in the process of growing. Griffith helps her out of a situation she's stuck in (imprisoned), but she makes the next move (declaring him her fiance, and therefore, next king of Midland) all on her own. It's a telling and powerful statement for her to make, and shows, I think, that she is, or at least has the potential to be, a capable ruler.

Griffith may not be the best choice, but you also have to consider, she hasn't seen the creepy, Lovecraftian side, and could very well change her assessment of him if she did. We just don't know that yet.