This is Lady Morthanlu. I got her from a Menagerist Goblin during Season 11. The Menagerist Goblins are the only type of goblin that drop pets. Kill the Menagerist Goblin – and it will drop a random pet for you.
The flavor text for this pet says: “Lady Morthanlu is the picture of sophistication and charm. Only the most refined adventurer will bring her along!” – Barker Chan.