Overview
C-93 is a buffing HG.
C-93 gives a weaker than normal Damage buff to all Echelon members, a short and small Rate of Fire buff to the 3 highest damage dealers, and an additional short and small Rate of Fire buff to allies who get debuffed. Her tile layout shifts the Echelon backline, which can be very awkward for kiting, especially when fighting enemies with piercing attacks.
With these things in mind, C-93 doesn’t really bring much besides being “better” when your backline gets debuffed, which is not a very appealing niche when you can simply use a regular buffer like Stechkin. As such, she’s optional at best.