Your post proves my point.
Cressida does not deserve such a scathing summation imo.
She was very 'young' (experience-wise, not worldly) when she came to him, and lets face it, he has to have chased her a bit (she had a boyfriend). There is nothing in Cressida's demeanor that would ever convince me that she is as conniving as you say. She fell for him and was giving up her life and ambitions for him when he (apparently it was his choice) walked away.
She has moved on and made the best of what he dealt her. That's being mature, not ambitious or conniving. :flowers
Although I don't like it, I think you are spot on.
Cressida (or her family) presented herself as a shy type who disliked publicity. But her actions after the split with Harry don't support this image at all.