Tell her what you told us.

I had a great father in my life, and I totally understand why this is difficult. I'm not sure why you wouldn't understand why having something like this happen would be painful, maybe you need to reread what's going on here. Someone who isn't even related to him that talks to him every day is asking his child who barely speaks to him at all what's going on with him. How would you feel knowing someone that isn't even blood gets your father's attention daily, and you get next to nothing after he left you when you were three? I'm not sure why you don't understand why this would be difficult, but maybe you're just wired differently than caring human beings with empathy.