My friend is mad at me because I can't donate blood?

I don't even understand why. I donated blood last February and ended up passing out for 20minutes. I was taken to the hospital and they found out that I was anemic and had Hashimoto's disease. So now I can't donate blood. I've tried to explain this to her but she tells me that I'm being selfish. I medically cannot donate blood and she cant get that through her think skull. She started yelling at me calling me a liar because she knows a few anemic people that donate blood. Yeah, if i was just anemic I would, but I also have hashimotos disease. She thinks I'm making it up...whatever. What can I do to make her see how stupid she's being?