She's pretty much garbage :) with her partner she's "okay", as a shield-ignore nuker, but ... still pretty bad.

Depending on how far along your account is, she can be a very strong addition to your Roster.  

HellHades rates her 4 stars, and you can see build advice & damage multipliers here:  https://hellhades.com/raid/champions/jetni-the-giant/   

Short answer on best build is probably a Hybrid of Damage & Accuracy, so you likely want Crit Rate Gloves, not Crit Damage because you need to use substats to stack accuracy.  Combine that with Attack Chest, Speed Boots, Crit Damage Amulet & Accuracy Banner.  

If you have the gear for it, a combo of Savage (or Lethal) & Perception would be good on her.  Otherwise, Cruel & Perception.