Bio: Gertrude was one of the Mole Men's many subjects, an outcast from the surface world, deemed by surface standards to be "ugly".
One day while the Mole Man was experimenting with the diamonds from the mythic Valley of the Diamonds (as seen in the original Fantastic Four #1) he discovered that they were actually supernatural in nature and that certain ultrasonic frequencies would cause the diamonds to "sweat". Believing he could use the liquid as a weapon, he created a vast amount of it. Gertrude slipped from above the vat of the diamond liquid and fell into it.
The Mole Man and his subjects and moloids believed Gertrude to have died as when they were able to get her out, the liquid had hardened into a cocoon around her. Their grief was short lived however as Gertrude broke out of the cocoon, completely rejuvenated and looking decades younger than when she fell in.
The Mole Man believed the liquid to turn anyone who was encased in it into the opposite of what they were. In fact, it brought out the "true" being within them. And Gertrude's inner being, her true self, was a beautiful young woman.