I don't have any credentials to answer this besides being a third-time mom, but my guess is yes it will screw her up today and maybe tomorrow but not permanently ;-) I have noticed that many sleep books (Tracy's included, sorry, although it's my favorite) are written as if the baby in question is your only child and your life revolves around him/her alone. For example, how can I NOT overstimulate my baby at activity time when the older 2 kids are around and dying to show off/hold/entertain the baby in their own way, and I want them to enjoy the baby and start building a relationship with him too? When you have older kids you can't totally be a slave to your baby's nap schedule--you accomodate it as much as possible but sometimes it is the thing that has to give. The baby will survive, although temporary messed up schedules and overtiredness might be the price you have to pay. Small price to pay for being blessed with each and every one of your children though!