I was afraid I was going to be completely lost reading the second book in a series first. I was in a way, but not in others. I do wonder why she's the seventh sister, though. I'm assuming that's what the title of the book means, at least. I know of two other sisters (Fawn and Clarity, who we meet at the very end of the book).
This book doesn't feel finished. I think that's the point, so you'll get the next one. Or, in my case, go back and read the first book and then go on to the third. I'm not too sure about going back to read the first one, although I did like this book.
There's a love triangle, again. I still hate those!