So I decided to run off with one of these OC concepts.
I am very well aware that she doesn't look like a full gargoyle at all, but that is very intentional. In the series, I remember that the London clan look more like mythical (or full) animals and have feathery bird-like wings compared to the Wyvern, Japanese and Guatemalan clan (Zafiro being the exception); so I thought, how about angelic statues? So I went ahead and gave her blunt fingers and toes, and extra pair of wings to keep her balance/for the sake of being able to manoeuvre (in the absence of a prehensile tail). This would mean that she isn't really the best flyer (in terms of speed) compared to her half-siblings, but her manoeuvrability is better than the rest of them, and she could fly instead of just gliding. The only clue about her race would be the number of digits on her hands and feet, and the lack of eyebrows and a bellybutton.
In a way, Palila (or Lila for short) is a very special kind of gargress.