The Blood Will Dry by Kate L. Mary

Five years after an alien invasion, the Earth is unrecognizable, and all Diana wants is to forget the past. After years of struggling to find a weakness in the aliens’ defenses, she stumbles upon a solution just as a new and more deadly threat surfaces. Faced with painful memories, an attraction she never expected, and a war most believe can’t be won, she and the other survivors mount a battle that may determine the fate of mankind.