Welcome to YT and congratulations on your new baby.
Small dogs have small bladders and need to go frequently. She is not going to be able to hold it all day, nor would it be good for her.
I am a strong advocate of not withholding water or food ever especially for a 3 pounder who is at greater risk for hypoglycemia. Water is crucial for the health of all vital organs and systems. A human should not be without water or bathroom for hours per day, nor should a dog.
I would strongly recommend using a piddle pad or finding some means to provide your baby with at least a couple of bathroom breaks during the day.