I'm sorry but I wouldn't interview without the child being present. For me, that part of interview process. I want see how child react to instruction, if parent step up when needed and redirect, if she has tantrum when asked stop whatever she doing and if parent cave to it. I want know if child is disrespectful to my house, going jump all over my couches, run around the house, torment the cat.
I understand too your thought that maybe exclude child for initial interview but really, how many interview level you expecting? I work long hours - 9 with children in my home, a couple more cleaning and prepping for next day when child gone. Add in interviews too, most often after hours and it long day. My time is precious and I'll be honest, someone who expecting to come out once for initial interview and then return and take another evening from family time to bring child, is what we refer to locally as a time vampire.
I know it big decision for you, but it is potentially two of our evening gone when it really only need be one.
One side issue to think about too - If you not planning to tell your provider until last minute and not give her any clue that this might be coming after she cared for your child for so long, then really it does give other provider's an uneasy feeling. Reality is, even with 4 week notice, it usually take longer than that to find new child. When a child leaves, it's rare that a new client is lined up and there's no loss of income. We always welcome a heads up or little longer notice and we've all been hurt in past where a client we believed we had a great established relationship with, gives us minimum notice. A new carer seeing this pattern might be a little wary of entering into relationship with you.