A House Divided — Vivian L. Holt

Cassandra sits in Heaven, watching the world prepare itself for war, when she overhears a prayer sent in praise and not anger. She spends years watching over Hawk Evenwaters and his wife, Elizabeth. But when Elizabeth decides to give up her life after being told she is pregnant, Cass is sent down to save the child as well as the nation. Hawk, however, soon finds he must choose between the life he knew and the love he has been granted.