Light sorc merc wep

Hi guys, quick question: there is any better wep or word for my def merc 2nd act nightmare, which is using insight in eth colossus voulge rn? better than this but way cheaper than infinity?

 

For a light sorc, there is no better merc weapon than infinity, period.
For a time, until you get the 2 bers, you can go with insight, but if you plan to play long-term with her (and depending where you farm), you should aim for infinity.