I'm so sorry to hear about Reba. The pain of losing a companion animal is almost unbearable. Keep the wonderful memories of her tucked in your heart.
Your son sounds like a wonderful and compassionate young boy. I think it's so honorable of him to have built a memorial for Reba.
I do believe the 3 deer were in fact symbolic, as they stood content and peaceful watching as you drove on.
Take care of each other -
kathy