Even as mature as you feel she is, I cannot see the benefit of having an 8 1/2 yr old girl witness mom giving birth.
You can't control how she will feel, if she will become fearful because you are in pain, how would she handle that and worst case, watching you actually give birth. You don't know that it would not scar her for life or somply be mortified at the sight of such.
Her own body will soon be changing and she will have enough to deal with as far as hormones, etc without having to recall visually the process of birth and seeing her mom in pain. Although it could possibly be a great way to instill birth control and abstinence, LOL
It is a very adult experience and as nurturing as she is, this is not a little deal like bringing tea or ice chips to mom.
I am in the camp where it was a private bonding experience for my husband and myself. I do not get why some women would have the entire town in the room to experience birth with them. It is not something I care to sit back and watch.
My suggestion if you want her to know more about birth is to let her watch TLC and National Geographic.
I do think it is great that you have a good relationship with her and have open communication. My daughter and I have a very open communication line, discuss everything, and I've answered her questions from day one very openly and honestly. You will need those lines of communication and good relationship as the next few years progress and your daughter goes through the tween, teen years.
How does your husband feel about this? I would think, awkward...
Bottom line...... it is your family, your choice. Best wishes to you.
ETA: Just as I posted I saw your SWH so I guess I really don't understand why you asked for opinions, thoughts, etc since you've already made your decision. TV and videos are 1 thing... actual blood and gut is different.