Did Pitohui have a special nerve gear?
She was using the original Sword Art Online Nerve Gear, which had the capability to kill you.

The difference with the Nerve Gear and the Amusphere are the safety mechanisms put on the Amusphere to prevent the software from killing you by inducing high voltages into your brain. This is also why Pito didn't get auto ejected when hyperventilating.

Yes, Pito using the Nerve Gear could still kill her, but GGO doesn't have the functionality to fry your brain when you die... (duh) like SAO did