I would challenge him to go follow one of her workers around for a few days. See what they see and do what they do alongside them. Then get back to me.
On the Amazon page for Hitchen's book on Mother Teresa, there are some comments from people who actually did work with her. They seem to agree with Hitchens.
Particularly disturbing is that money sent to help sick children under the care of Mother Teresa was diverted for other uses. She had access to vast amounts of funds but apparently chose not to spend the money on even modestly improved medical facilities that would actually have saved the lives of the people she was caring for.