In the part where you have to fight Zanik, you are supposed to tell her something every time you kill her.. I simply don't get that option..

 

I kill her, then she sais "you're stronger than I thought, human." Then the dialogue box disappears...

 

 

Any help, please?

I think the best you can do is time your attacks so they come right after Zanik's. That way, her last attack won't interrupt the dialogue that comes up when you deplete her hp. In the meantime, you should send a bug report to Jagex about this.

I had the same problem. Had it in high definetion so I changed it to standard. Worked just fine after that.

 

Thats not the only quest I've been stuck on in high def. Recently did rocks away and no matter what I did I couldn't finish the hand puzzle. Changed to standard and did it straight away.

 

Oh well hope it works for ya mate.