That's very bitter sweet...
She is marrying a boy her own age, i have no issues with that. I think it's wonderful that her family are able to fulfill this last wish and her parents get to see their little girl have her wedding day... every parent of a daughter wants to see that!
I spent 5 years working with a children's hospice service providing palliative care for children in their own home. Their emotional strength and maturity is really amazing. The families are also really special because they know what is really important in life and have an amazing bond, it's very inspirational.