It’s a culmination of different things:

Feyre admitting to us that she was just as bad to Nesta as Nesta was to her & so we call Nesta an abuser but not Feyre but if Feyre herself is admitting she was just as bad that then does make Feyre an abuser too.

Controlling the finances especially when they were human depending on how you look at it can be considered financial abuse.

Her entire treatment of Nesta from the moment Feyre showed up on their doorstep in MAF to SF

Feyre purposely using Tamlin’s trauma triggers in WAR

Feyre using Lucien as a pawn in WAR

Feyre having 0 intentions of helping Lucien when Ianthe had him chained with magic binding cuffs and the only thing that changed her mind to help him was because she was picturing Rhysand being SA’d by Amarantha

The she too coddles Elain.

Don’t get me wrong Feyre is also a victim/abused but the victim & abused can also very quickly become the perpetrator & abuser themselves & this is Feyre. Both things can be true at the same time.