The heroine is a twin, and has always been the timider of the pair; her arc has to do with her learning her own strength.
I'm definitely reading the others in this series.
One plot thread I thought was going somewhere, but didn't, was a dog attack on the heroine and her friend when they were children. The friend was killed. I immediately wondered if it was supposed to have been a hellhound attack, perhaps aimed at the heroine, but it didn't turn out that way, at least not in this book. Which is fine, but I spent too much mental energy speculating about it while reading.