When She Was Me is a fast-paced psychological thriller, and what this book successfully achieves is the perfect isolated setting. It is based at a campsite with cabins in the woods, and it was very atmospheric and mysterious. 
It has dual POV between the main characters who are twins, Cassie and Lenora, with interspersed chapters which are flashbacks from an unknown narrator. It did hold my intrigue throughout, but it did feel very repetitive and I just wanted those big reveals and twists, but when they did happen it felt anticlimactic in my opinion. It did have a tense ending which I thought was well done but I didn't think the 'epilogue, HEA' was necessary.
I personally think this book needs a trigger warning list, as for me there was unexpected content which made me feel very uncomfortable and I wouldn't have picked this title up if I knew about it. It actually turned out to be a twist which I think was handled poorly. I know some readers are not a fan of trigger lists because of spoilers, especially in thrillers, but I would have appreciated one for this book. 
Whilst this wasn't the book for me, I would still recommend it to fans of isolated thrillers if you are looking for a quick, nail-biting read. It is a debut and I would try out this author again in the future.
2 stars

Thank you to NetGalley, Poisoned Pen Press and Marlee Bush for the opportunity to read this advanced reader copy.