Why Grandma used to say I was a spoiled brat, why the sudden change in her now that Im a teen?

Grandma might be more polite than you notice. You might still be a spoiled brat but it is no longer her job to tell you so. Glad to learn that One does not throw temper tantrums any more. Maybe you are growing up a bit. Good luck... most grands wish for their young-uns to grow straight, smart & mindful.