I'm so sorry too.
It always hurts losing someone you love, and time is the only thing that closes the wound at all. Later, when your mom has had some time to recover, she will remember the ten wonderful years she had with Heidi. While it is awful that your mom had to see Heidi's body, I would take some comfort (much later) in knowing that her death was probably instantaneous.
My thoughts are with you, your mom, and beautiful Heidi.