Everyone has to gain experience somewhere. She's fresh out of childcare courses and will have less bad habits and jaded thinking, more patience and energy to handle an energetic baby that will be walking in a matter of a couple more months. Plus, you will be offering someone a chance to gain professional experience in infant care that will look very good on her resume.
Call some other agency inquiring about prices to get a good comparison. When I was looking for childcare, nannies cost double the minimum wage. which was about $16 /hr at the time.
If you're still iffy, ask the agency about trail runs before you commit.
Nannies who are used for the long haul can develop deep bonds with the children they care for. And sometimes they can be considered part of the family. So, choosing carefully is crucial to ensure your kid isn't going through a succession of different nannies.