Why would a doctor give injections to make non contagious TB contagious? This is happening to my grandma, who is in her mid-80's.

Misunderstanding? This is not clear to me. There might have been a misunderstanding of the treatment and goal. It is best to discuss it with your grandma's doctor and ask your questions and ask for clear answers. It is best that all people involved have a clear understanding of the treatment.