Yes it's true, Pinkie Pie has a mother and this is what she canonically looks like.

Before I move on, let me just say I do not support Newborn Cuties, and I do not think it's good by any means, nor do I defend it, but it did introduce some interesting concepts. One being Pinkie Pie's mom being shown:
Screenshot

And another potentially explaining how ponies reproduce: by rainbows. It's how Sweetie Belle was born. It's not clear that this is how all ponies are created. It could be only unicorns, or only Sweetie Belle. If all ponies are created this way, it would explain how they are able to reproduce with no males in their species.

Anyway... this is Pinkie Pie's mom in classic G3 style, and made her old because Pinkie Pie is an adult pony at that point. Also because they would look almost exactly like each other if I drew her in the normal age. I took some of the ideas FiM used to make Granny Smith look old by making her skinnier and her legs slightly knobby. I also pictured elderly ponies' hair to be not as bouncy, and added some crows feet to her eyes and gave her a fluttershy-like eye shape.