It's going to take a while. Abuse victims often love and feel a very strong sense of protectiveness towards their abusers. She most likely loves him even if she's unhappy with some aspects of his behaviour. As he's had a troubling time the last few years he might have made it clear either overtly or through implication that she really was an escape for him, or she was the only person he felt safe with, etc. Right now she's probably feeling horrible because she's imagining that he's been through all of this stuff and now he's being punished further, and kept apart from her, and she probably feels like it's not really his fault, because of what he's been through or because he's still figuring things out and didn't understand, perhaps because she feels like she had a bit of a hand in things too or encouraged him, and she'll be feeling a bit panicky that others don't understand him like she does, so on top of all of it he's going through it all alone. And at 14 it's so so common to feel as though you know better, feel deeper than all of these adults who are being really harsh and uncaring and they don't understand, they don't take a 14/16 year old's feelings seriously, but they are really serious. Basically, she won't see him as a calculating abuser, she'll see him as a wounded hurting young man who only did what he thought was the right thing and is now being thrown to the wolves. And you can't hope to change her feelings on that, for a really long time. She'll only see his true actions in hindsight, most likely years down the line. What you can hope for sooner is that she realises how trapped and unhappy she felt within the relationship and how much better she feels out of it, though this might be still tinged with guilt, like she feels better off without him but she thinks that he feels broken without her. If he moves on fairly quickly, she'll probably let go of that quicker, because it will be a rude awakening to what she really meant to him. But if he wallows and really seems upset by this (and you can bet she'll be kept up to date about him by her friends etc, even if you don't allow contact) then it will take much longer.
When I was in an abusive relationship the thing that kept me close to my mum throughout it was that she understood that mixture, which in hindsight was because she still had (Still has) an abuse victim mentality too. She never criticised HIM directly, always acknowledged my love for him and really understood how that felt while managing to enunciate how he was hurting me too. She used to give me tips on how to manage it or how to communicate better with him, which I'm now really shocked by, but she thought that she was helping. In fact, she ended up getting sucked into the sympathy thing as well and now far beyond the point where I feel anything for him at all she still has him as a friend on facebook and I think still feels a bit sorry for him. She believes I was right to leave, but she also has sympathy for him as a person and not really understanding why he keeps getting into the same situations.
So long term, not massively helpful. I imagine it's probably a bit early and she's still a bit raw, but I think it will help her a lot if you can communicate to her that you understand that she loves/loved him, the person, if not the actions. And that you're sorry that you had to go over her head and cause both of them pain and anguish but that sometimes as the adult you have to step in. That you don't expect her to understand or forgive you any time soon but perhaps one day she will. And that you will always love her, no matter what happens, which I'm sure you're telling her already. And then don't ever ever be tempted to say "I'm so glad you now see how bad he was for you" until the day that that conversation is totally, 100% instigated by her, because the process of her recovering and getting over the relationship is slow, and back-and-forth, and it's likely that for a long time she'll seesaw between feeling glad and feeling guilty, between missing his good parts and relief at being away. That's so confusing and hard to deal with, and any encouragement of the glad/relieved parts seems to push the others to the surface, as though they are saying "But me! Don't forget about me! What about this!"
You have to wear the bad guy cape for a while, and accept that it is part of loving her. She will appreciate it, but she can't now, because she is hurting. This is where it gets so very hard, but you are doing absolutely the right thing. Please push through, and hold on. She does love you and she will come back. Just as toddlers sometimes hurt themselves through being overwhelmed and we have to take control, which they hate, and stop them from hurting themselves, which they hate more, you are doing SO well by being the unmoving rock here. You take control because she can't, and she will come back. Just like the toddler, it just takes longer. Hang in there! You're a great mum. 