Let's be totally honest: Ellaria Sand had her panties in a bunch since day one. Being a bastard never sits well with anyone in GOT and the trend continued when she had four bastard kids of her own with that handsome devil Oberyn Martell. But once her lover Oberyn is murdered, Ellaria's true colors really come through.
Although she's pretty tame when it comes to her own daughters, the same can't be said about Myrcella Baratheon's case. In a totally uncool move, Ellaria poisoned Myrcella (Cersei's only daughter) to get revenge for Oberyn's death, aka Myrcella had literally nothing to do with it. How she actually killed her is also SUPER sneaky: she coated her lips in poison and kissed Myrcella goodbye. Once Myrcella was out of sight, she took an antidote and ended up just fine. Myrcella on the other hand, died painfully on a ship, making Ellaria BEYOND extra.
She also used her daughters to create a pretty fierce fighting girl gang who know their way around giant knives, which is pretty epic. For these reasons Ellaria comes up the fifth spot.