I always found the accusations of Diana's charity work to only be a ploy to boost her image far-fetched. Since she was a child she had a knack for helping others.
The "accusations" weren't all made made by fanciful writers. The man in charge of AIDS Trust was among those insiders who went on record about how he felt Diana used AIDS patients during engagements on behalf of the cause. I don't recall his name, but here is a photo of him at the last engagement he invited Diana: Getty Images - Diana Aids Trust (he was standing behind the girl presenting flowers)