Thank you DBlain.
I contacted the second lady the one that was meant to take care of him and told her my concerns and she replied: "Say no and lock him in your laundry area", nothing else like she did not care much about how I felt.
Some other friend suggested she tricked me into sitting the dog because she had plans for the weekend and the dog was in the middle. Don't know if it's true or not but just the thought that a "friend" whom I put my trust to take care of Lucy could just make other arrangements without my consent....
Anyway, I have no choice but to wait for his mommy to come and pick him up and keep and eye on their play time because he also eats her food and water. This will teach me a lesson though, I will have to learn to say no and hope to keep the friendship.