i think the BEST thing about bringing a new baby home is watching the older siblings .. the pure Joy and excitement you see in their little faces.. they are the only ones that have no expectations on how this whole new baby business will go down they just love the baby for.. well being a baby!
My Ds's were the same age as your DD when we bought home the next bub iykwim and they were so proud to show off their new.."toy" lol
Sure some bits are hard, kids dont read the rule books but looking at the way they try and interact with bub or they way they simply look at them makes it all worth it!
Good luck... But i dont think you will need it!!!