It feels like people equate cancer with don't-invite-anywhere! She has cancer, not some contagious disease!
Ask your friend with cancer if she'd like you to host a small get-together. Simple, small and easy are the key words here.
Having cancer is isolating because most people think, "Oh, she's sick. I can't invite her." Or "I don't want to make her feel bad by inviting her when she can't come."
So instead your cancer friend feels hurt which is caused by your fear of hurting her feelings!
Do not assume anything. It makes an 'ass' out of 'u' and 'me.'