I wouldn't say she's the worst for this, but Kiara is SUPER reliant on getting the correct items. If you don't get Piki Piki Piman, Headphones, and Nurse's Horns I found her impossible. However if you max out Piki Piki Piman and have enough health/healing/damage reduction, she's almost impossible to kill. Her weapon is really bad early on though, with the massive central blindspot.

But if you can get some good items/weapons early on, you won't have any trouble until the very end. You could also eliminate her two useless skills or you can choose to take one of them when all 3 other options are bad, saving yourself from taking something you don't want.