Worried about my sister

Not used to writing things down like this instead of just worrying inside my head so I'm sorry if this sounds (reads) convoluted.
The title says a lot I suppose but for the sake of clarity I want to explain some things from the beginning. paint a clear picture if you will.

My sister, who I'll call Anais, now 24, was in a relationship with a man I'll refer to as George from the ages 16-21. it was a long, tumultuous, period. she would often come running home (the two of them lived together for some time) crying, at first she would refuse to talk about what happened (as she felt that was "betraying" him) but in time it became clear George was abusive of her. in different ways. he would be controlling, jealous, domineering. even when they were still teens there were subtle signs that only grew more apparent.

she told me of times where he would lock her in a closet for hours until she had to pee on herself. where he would put cigarettes out on her if he had too much to drink and lock her out of their apartment in the pouring rain. instances where he would beat her, throw her around, make her sit still on a chair for hours and make her say stuff that wasn't true (make her confess to cheating for example, even though she hadn't).

three years ago now things escalated so badly anais had to go to the hospital and George was arrested. being in the hospital was what made anais snap out of it and understand it was going to be away from him or into an early grave (which is a quote from her- something she said to me as she was laying in her hospital room, with a black eye and bruises all over her body).

George went to prison for what he did. not long enough in my opinion, but he did his time. for anais this time has been really challenging. she lived with me for most of it.

a little over a year ago, she met Louis, her current boyfriend, who is a delight. he is super gentle with her and totally accepted my "big sister interrogations" I subjected him to early on. he was understanding, empathetic, honest. they have been an official couple for a while now. they do hobbies together and Louis plays a big role in her healing, anais does various sorts of therapy (like art therapy for example) and louis hangs all the paintings and artworks she makes up in his home. all that to say, imo, he is perfect for her. she agrees with that too.

two weeks ago, everything was shattered with the news of George's release. the time he was sentenced to has passed and he was let out. for anais this was startling, insane, life destroying, maybe. the day he was let out she locked herself in her bedroom and refused to come out. would not talk to me or louis or our parents who have also been super worried.

then last week when she seemed to be doing better she came home crying again after being out all day and confessed that she had been calling the prison asking about him, his old phone number repeatedly, and even phoned his parents to see if they knew where he is now. She was a total mess, crying and apologizing and insulting herself. I didn't tell Louis.

Two days ago then, she had a therapy session scheduled, which I thought was great for her. I felt she was in need of that, to talk to someone who knew her perhaps better than we do.

Then she stayed away. For hours. She left in the morning (10) and in the afternoon, at around 2, she was still away, which is not normal for her. I admit it's not the best thing I could have done, but shortly after I called her therapist and she told me Anais had called in sick. That being the first time ever.

At 6, Anais came home looking like a shell of the woman she is. I had of course called Louis who came over to mine as we waited for her to come back together. She wouldn't say anything, she seemed hostile towards us, telling us she was a grown woman, she could do whatever she wanted - which is absolutely, 100% true, but I tried to convey to her we were just worried. That we knew it was a difficult time and that we understood her feeling betrayed, sad, angry, maybe at the fact that he was out.

she said that she had been having the urge to see him since the day he got out for closure, then explained that she "just" wanted to see him to know for sure if he really "gotten better" and had been "changed" in prison as she believes the prison system is for, wanted to see if he would still hit her.

She had somehow figured out where he was now and had gone out to see him. Waited for hours to catch a glimpse. She says she didn't talk to him, just followed him around, wanted to know what he looked like now, what his life is like, where he lives.

I think I may sound overbearing and I don't know as well as therapists do what "normal" behaviour is for someone as deeply damaged as my sister, but I do know that I have seen this behaviour. the wondering "would he still do it?". I have seen her wonder this aloud before, and those times, she went back to him.
I don't know what to do. If there is a little belief in her heart that he wouldn't again I know she will take him back in a heartbeat.

Louis and I have considered reaching out to George himself. It's a terrible idea, I think, but I'm hopeless. I want to protect her but can you really do that?