This is a reference to the mythology of Nephthys disguising herself as Isis to seduce Osiris, as well as the fact that they are both Level 5 and have similar stats.
The two cards are also mirror images of each other, with Nephthe having a moon in the background while Eset has a sun. They both have similar coloration and posture as well, hinting that these two dragons might be twins.
Like her sister, this card has a helmet image bearing a hieroglyphic symbol. In this card, it is the throne symbol of Isis.