I would say that if she wants to go she should. From what you said she seems mature enough to know what's happening.
When i was 13 my Dad (by then he and my Mum had split up) was sentenced to prison. He didn't live with us then but I still saw him fairly regularly. My Mum wasn't keen on me going to see him but she did eventually arrange for us to go. I had no idea what a prison was like then and was a bit scared but it was alright. I remember getting searched going in but it was good to see him. He was in for 3 years and I ended up going to see him every few months. I was glad that my Mum allowed me as I could stay in touch with him while he was in prison. I think I would have resented it if she hadn't let me and I know it was a big thing as she had to come to and they were split up. I remember seeing him there in his prison uniform and being real sad at the end of the visit and promising myself that I would never do anything that would make me end up in there as I knew it was hard on him being there.
Unfortunately life doesn't end up going to plan and I did some stupid things when I was 19/20 and ended up getting into trouble and I got 18 months myself. After a few months in Young Offenders I got transferred to the same prison as my Dad had been in years earlier. I lived with my Mum and her new partner and my 2 younger brothers. They were 14 and 16 when I got sentenced. We were really close and they looked up to me so I had really let everybody down and felt really bad and ashamed. I know my brothers wanted to visit me and I remember my Mum not wanting them to visit me - maybe because I had visited my Dad when he was in prison and now I was there years later. Eventually she allowed them and it was good to see them but I think it was the right thing to do as I was able to tell them how tough it was and how bad I felt and they were able to see it wasn't a holiday camp like the papers say.
They are 19 and 21 now and as far as I know they haven't been in trouble with the police at all. It was also in a way good for me as it got me thinking about how much of a waste of time prison was. I remember when the visiting time was up thinking about them going home and having a good time while I was going back to my cell. By keeping in touch with all my family it made me more determined not to let them down again. Even with my Dad who came to visit me when I was there - was strange that a few years earlier I had been visiting him in the same prison and now he was visiting me.
Looking back prison was good for me as I had plenty of time to think about what I wanted to do with life and that I needed to change. I've not been in trouble at all since getting out. I'm working away, have a great girlfriend and a baby on the way. I have a good life now.
Anybody can make a mistake. Good luck with your daughter and hope things work out