By saying "in her ashes she lies", Shakespeare signifies Cleopatra's transformation into a symbol of destruction, beauty and passion, and the ultimate end of her reign and influence. The word "ashes" carries a strong connotation of mortality, decay, and the impermanence of life.
The idea of "ashes" also highlights the destructive nature of the love between Antony and Cleopatra, as their intense passion and desire lead both to their downfall. Through this phrase, Shakespeare evokes the emotional impact of Cleopatra's tragic fate and the profound sense of loss and finality that accompanies her death.