First let me say I TOTALLY understand not wanting to rock the boat.
What do you think she'll do or say?
Is it not wanting to hurt her or set her off?
What is it that you are resisting?
What happens in your mind when you play out you telling her, "I don't trust you. You're not safe to watch our child. I've made arrangements with the daycare and it is NOT an option to do anything else."
What do you see happening and how do you feel about it?