Trial run with our new nanny is scheduled for tomorrow :)

I am excited to get to do a trial run with a new nanny tomorrow. She seems like she will be a good fit so far, but I would like to see her in action and give the kids a few hours with her to get to know her as well. I was originally planning on just leaving her at my home for a couple of hours and running to town, but I would kind of like to see her interact with the kids a little too. So maybe I can hang around while she does lunch and then leave for playtime before naptime and come home right before she lays the girls down for their nap. It seems foreign to me to interview and hire a sitter since I haven't done it more than twice before, without it being someone I knew really well or someone that was family. She has a CPR/First Aid certificate and is a certified lifeguard as well. She doesn't smoke, is studying at VT towards a pre-vet degree and already completed part of her schooling at her local community college in NJ. I really hope she ends up liking the family and we end up liking her just as much, but this time around I have been very cautious since the last two "regular sitters" that took care of Aiden left me with a bad taste in my mouth and the girls have never been watched by a sitter. I feel like there are questions that I am leaving unaswered, but have no idea what other things I should ask her about. She has given me references and I want to call them, but I really don't know what I should ask them. Can anyone give me some pointers? Is there something I am overlooking or am I just supposed to be paranoid?