I'm going to catfish a friend to convincer her to break up with her emotionally-abusive boyfriend.
Why are you going to use catfishing to do that?
Recently, she told me that she met a guy, and I suspect that she's going to start going out with this abusive guy soon.
It's good that you are concerned about your friend, and if you have doubts about this guy, you should let her know.  However, it is wrong to be deceptive, and to try to convince your friend that you are someone else, even if you do so with good intentions.
The catfish will only chat with her for a couple of messages. Then, I'll share photos of me and let her know who I really am.
You should just talk to her as yourself and tell her how you feel about this new guy. Going the catfish route can break your friendship and is really mean to do to someone.