She wrote: Your father wrote back.... Then you were born... Sounds to me that she is speaking to Barack II otherwise she would have said your grandfather wrote back.
That’s how I read it!
You read it incorrectly. Yes, she's speaking to Jr., but she's saying Barack Sr. wrote back to his father (Bambi's grandpa), telling him he's going ahead with his plans to marry Stanley, despite the Barack Sr.'s father's objections.
This isn't complicated.