Your parents have come to a point where they have nobody to watch you, and they really need someone... so it comes down to you finally being introduced to your Grandmother. They kept you from meeting her because she has a lot of troubles accepting the reality of her own age. Being a GRANDMA?! No way. She wants you to understand off the bat that she doesn't want to be called that word.

You call her Grandma though, as it's what your parents have told you to call her. But she pushes back, insisting that her body is not saggy and her face is looking youthful and she's really not all that old to begin with! She pushes and pushes, slowly finding herself more and more ready to prove it further - so she does, and strips out right in front of you.

It's clear why your parents were hiding you from her. Grandma is a little off!