As Francescasmum says, this is the way things are done so just relax and let your DD do her thing.
Lots of NAPMs have tons more experience than I do, but here's my five-penny-worth.
From our experience, your DD will be asked to perform the lines that have been sent to her, so it's best that she memorises them, but don't stress about it as they won't mind if she takes the script in with her either.
She may be asked for ident and profiles - usually that means saying her name, age and the name of her agent to the camera and then turning left and right so they get a shot of her face-on, and in profile. Don't worry if they don't do this, but it's good to be prepared in case they do. This is the only time she should address the camera and look down the lens. Otherwise, just forget that the camera is there.
There is no need to over-prepare, but it might help your DD to think about the character she is being asked to portray so that she can deliver her lines as the character would - in other words, acting.
Don't worry about where the camera is. The casting assistant (rarely the casting director unless she gets a callback) will put her at her ease and tell her what they want and will probably read with her. They are very good at this.
She may be asked to respond to a couple of redirections. So, for example, if she has played her character as sad, they might ask for angry, or for even more sad, or to move differently. Again, don't worry if they don't do this, but I'm mentioning it because sometimes the child thinks they've done it 'wrong' when all the casting assistant is trying to find out is whether they can work with direction and whether they can portray more than one emotion.
It's unlikely to take more than 5 -10 minutes.
Of course, your experience may be very different from this, so don't worry if you find it set up very differently or if it takes more or less time. But do let us know - its good to share!
Flo did one recently (which she said went badly...) where she was asked to play the role 'girly' then 'girly but fearless' which she found a bit confusing. Then she had to react to an imaginary object, so a few improv skills don't go amiss. I don't think she has ever been given props to work with.
We've also had experiences where they have taken the kids in in groups/pairs to perform a scene. On one occasion, the girl Flo was paired with didn't show up, but Flo's little sister stepped in, even though she had 'retired' from acting a few months earlier. It's good to be flexible! Having said that, Flo didn't get the job
The best advice you can take is to relax, take a leaf out of your DDs book and be totally unfazed. It's great that she is being considered and fingers crossed that she gets a callback and maybe cast in the role. But, as with commercials, they see lots of kids and you may hear nothing.
However - here's the thing - even if she doesn't go forward with this role, the casting assistant/casting director will probably be casting many other projects and it's not unusual for them to recommend kids they've seen in one context for another.
Good luck - hope this helps and do let us know how it goes!
Deb x