Keep in mind that Mayuri did say that he was carpet bombing the area with highly concentrated anesthetic that was potent enough to effect him too. So by the time she stepped in he was probably sluggish and likely not capable of fighting well anymore. His gambit failed and she stepped in to compensate. Pernidas killed her, but she did in fact kill him on her own thanks to the gland Mayuri put in her, giving Pernidas turbo cancer.
Keep in mind that Mayuri did say that he was carpet bombing the area with highly concentrated anesthetic that was potent enough to effect him too. So by the time she stepped in he was probably sluggish and likely not capable of fighting well anymore. His gambit failed and she stepped in to compensate. Pernidas killed her, but she did in fact kill him on her own thanks to the gland Mayuri put in her, giving Pernidas turbo cancer.