How am I suppose to save kerah from Cet's influence. Is there a scroll or a spell?

Holy Water, Batman!

You need to dip an empty flask into that big pool near the start of the pyramid. During a lull in the catfight with Kerah she will say she is thirsty, give her the water and she should be cured.

Warning: This part of the game causes a freeze up for many people (me included) be sure to save before you trigger the portal 'cos you may have to replay it a lot to get through.

thank you for the help and the warning. I needed it.