Wow you brought back a memory I didn't even know I had. Writing about father's day, which was then shared with the class. I remember wanting to have my dad be as wonderful as anybody else's, which added to the need to embellish. Peer pressure. May or may not be true for your daughter. Just remember they also live in a world which we are not part of--school.
Your daughter knows the truth. If while young she needs this imaginary version of her dad to help her get through life, so be it. Doesn't change her reality with him, and she knows that too.
If he fails to see them, and that note she wrote is never given to him, keep it put away somewhere for her. One day she might as an adult want to discuss the past with you.