S.K.
When did they start childcare? Ask them to tell you why and how they started and how long they plan to provide care.
Ask them if they prefer to be called a caregiver or a babysitter. This will show you if they take pride in their services or not. People that think of themselves as a babysitter are not going to provide as much in the way of teaching and they might not provide as much personal attention. Babysitters are just there to keep them safe, clean, and fed. Caregivers pour a LOT of their time, effort, and souls into their businesses.
Ask them how they decompress at the end of the day and how they handle frustrations when they are with the kids. They should be able to tell you how they handle their own emotions when life gets rough. Children are a mixed bag of blessings that include times of feeling overwhelmed. If they deny having these feelings, they aren't being honest.
Ask them how they handle a baby that is crying every time she puts the baby down. Do not think that your baby could never do this. Many babies that have been the sweetest and most laid back babies at home have become obsessively clingy when they start a new daycare. You and this person need to be on the same page about how to get the baby through this time. She will need to care for the other children and she will need to make and serve meals and visit the little girls room. So she needs to have a plan.
Ask her how she handles children that are aggressive and how she will keep your baby safe. Obviously, babies are defenseless and often older toddlers will go through biting and hitting phases.
Ask her how often she gets sick and if she or her own children are susceptible to common viruses. For instance, some children get strep throat all the time and some never do. If a person gets enough rest, drinks plenty of fluids, eats well, and lives a smoke free and alcohol free lifestyle, I guarantee you that they get sick less often. Find out how she handles sicknesses, for her, her children, and for your child.
Ask her what she feels sets herself apart from other in-home caregivers. She should have an idea of what services or policies she has in place that are better or different than most others in her area.
I could go on and on about this topic. I personally think it's a great idea to ask many of these things and so many more through email first. That way, you don't waste time meeting with someone that's not going to work. You can narrow down your choices before you start to meet people. Also, you can spend your time during the interview just really getting to know each other. Your instincts will sway you. :)