Good for you! We sound like we have some stuff in common....
My DD was 2 1/2 when our 2nd was born. We still tandem nurse and we all co-sleep. It works for us.
I am a Bradley teacher so I think I know where you are coming from.
My DD is fascinated by birth, babies, etc.
I would recommend bringing her along to some birth classes if you are doing this but mostly just talk about birth and how it works. Videos are great. I have a really good Bradley video of children at a birth so they can see how it all works. Explaining to her that mommy will be working hard and making noise is helpful as well as well as being able to explain the blood and fluids. You know her best- will she be upset if mommy looks uncomfortable or will she be helpful? I found that my daughter who was with me during labor (but not the birth) was very empathetic and know others who rubbed mommy's arms and head and comforted her with cool washcloths.
I think it is really important to have someone with you guys that can solely focus on your daughter. If she gets bored or wants to leave-- you don't want your husband/partner having to leave with her. Doulas can do this... family members... someone she is comfortable with. Most hospitals will require this. Most hospitals will also not let her stay overnight with you guys either-- so be aware of that.
My daughter stayed with our best friends during the delivery (her name is N. too!) and joined us in the room about 10 minutes after her sister was born. It was wonderful! I wanted her with us but my husband wasn't comfortable having her there during the birth as he thought he wouldn't be able to focus on me and the new baby because he'd be concerned about her.
If you want to talk about this more-- PM me and I'd be happy to talk.
Studies do show that older siblings who attend siblings births tend to have less jealousy, etc.
And just think about what you are doing to normalize birth for her!!
Good for you!