i have to say i think it would be unfair for the child who would be leaving in March to have to transition to a new provider for 2 months then have her life turned upside down when mommy brings home a new baby. I personally would try everything I could to keep the current family until March. I am sure there will be more families who need care with a March start date.
Sorry i hope i don't sound like a hater just thinking of the best interest of the child.