Hi Arvon! Fighting the Naga is admittedly a difficult task. And as Knarfling sais, she is virtually immune to magic. Here are a few hints on how to tackle the Naga, even with a low level party.
Get in really close to her and fight her in hand to hand combat. She won't use her gaze attack then. Her poisonous bite is dangerous, but she signals her strike by pulling back her head, so when you see her head moving backwards back away and she'll bite the air instead
Then move back in and continue hitting her. Repeat that process until she's dead.
Using this technique I managed to kill her with only one player character - at that time being a Warlock. Because my magic attacks were useless I stabbed her to death using ordinary daggers.
//Jazzid