Hayley, I agree with slyder, you do what you have to. I will most likely have to go back to work quite early with our next bub too. You have to pay the bills and live, there's no other choice.
Maddie will be fine I'm sure. She will probably love it. And starting at an early age, you will (hopefully) not have to go through separation anxiety! I am an early childhood teacher and we have lots of babies start at a young age. They have all benn fine. It's usually the mummies that are a bundle of nerves!