Not a stupid question at all OP.
I would pick the candidates that seem like they would be a good fit for your needs, and phone them & speak briefly to them. Make sure you are all on the same page regarding payment amount, childcare philosophies + that your personalities do not clash.
Once that is established, then you can have them come over to meet w/you (and your child(ren) as well.)
See how comfortable they are around the kids, get a feel for the type of personality they have and see how well you mesh w/them on a personal level.
It's okay to ask them to come over for a personal interview prior to hiring, many families require this.
If things go well, ask them if they can provide a few references for you to call as well as information from them for a standard background check.
Once the checks come back clean, then when you need a babysitter you can call her.
Hope this helps.