Poor little love, her cat died and she's been crying her heart out all afternoon.
cry (one's) heart out
To cry for an extended period of time. Poor Jane really cried her heart out during the funeral service.I can't watch those sappy movies because I just cry my heart out every time.
cry your heart out
or
sob your heart out
INFORMAL
COMMON If you cry your heart out or sob your heart out, you cry a lot. Note: The heart is traditionally regarded as the centre of the emotions. I threw myself on to the bed and cried my heart out.I had never known her cry, and here she was sobbing her heart out. Compare with your heart out.