When I was a baby......

A is becoming more and more firm that we knew her when she was a tiny baby - before she had teeth, could walk, wore diapers, etc. I have been correcting her, and telling her all the baby-like things she WAS when we met her, but I don't want to perpetuate her fantasy. But she is insisting, and it seems very important to her. I don't know whether to temporarily ignore it, or to continue to gently provide the correct information. She completely ignores me when I talk about her Ethiopian mom, or mention her name, like she didn't hear what I just said. She doesn't deny it, she just won't acknowledge or discuss it.