I wouldnt not just yet, id at least wait untill bby no longer needs night feeds ! Good luck wat ever you decide
I have four younger brothers and sisters and I remember loving being able to have my little sister in the room! You should just do a test run when the baby comes and see how it goes!
Id say its too much 4 her to handle shes only 3 & still needs a good nights sleep to be able to function & concentrate properly ! Think back when you had her as a newborn its tiring looking after a newborn day & night so let her get her sleep & let her help during the day :)