Re: Sick baby?
What is the cage temp? ( hedgehogs need warmth, generally, most keep at around 75F, as they can go into hibernation and lack the ability to revive from it)
What is the light schedule? (mind you, this wouldn't play much into what has happened since you just got her, but for future reference, they need 12-14 hours of "light". most here just set a small desk lamp on a timer, mine's on from 8am-9pm)
Have you tried taking a warm towel and massaging her belly to try to stimulate her to poop or pee?
Either way, another vote for the vet.
Depending on when you get the appointment, be sure to have syringes and eyedroppers handy as she can't go for too many days without eating and drinking. For food, you can either pick up Hills A/D from the vet, or just crush up her current kibble and soak in hot water until fully soft and easily syringeable. It would be wise to turn up the heat in her cage as well, perhaps even putting a human heat pad under the cage.