This is something that she has to come to terms with herself. Keep being supportive of her. Have her help you as much as possible with baby work (putting the pamper in the diaper pail, fetching wipes, helping feed the baby or atleast helping to prepare the bottle if the baby uses one.) Any time you feed the baby make sure that first you get your big baby a drink and/or snack. Have her sing nursery rhymes with you to the baby. And if you're just chilling infront of the tv, put the baby on leg and the 4 year old on the other leg. Right now, one on one time isn't as important for the newborn as it is for the 4 year old, so try to include the 4 year old on what ever you're doing with the baby, and when the baby sleeps give your 4 your old your undivided attention. I can't stress enough how important it is to let the 4 year old do as much WORK as possible in reguards to the baby. Kids aren't big on chores to begin with. Eventually she'll get tired of having to do so much and will only look to her new baby for someone to play with. As far as her regression...yeah, alot of kids do that. She'll get over it in time. But right now you have alot of work to do with her and the baby and you don't have time to be scrubbing poopy panties. Don't get angry when she poops. Just tell her that she's a big girl and doesn't need to poop her panties because she already knows how to use the potty and if she's going to poop in them, then she's going to have to learn to scrub them out herself. Teach her how and make her do it. I give her about a week, maybe 2 at the most and she'll stop pooping her panties because she won't like having to scrub them out. I often refer to my newborns as "Your baby" to my other kids. "your baby is hungry, should we make him a bottle?" "your baby pooped. Can you get him a diaper and the wipes so I can change him for you?" It gave them a sense that the younger sibling belongs to them as much as to me. My kids, while they pick on each other often and frequently, they are very protective of each other and very willing to help each other when the help is needed. Stay consistant, stay involved, and get her involved as much as possible. Make her feel like she's a very important person in your life and in the baby's life. Fake being tired or sick if you need to so she has to get involved. "Mommy doesn't feel good can you go give your sister the pacifier for me?" It'll make her feel needed. But anyway...she'll come around. It just takes time. And you might want to stress things when she does them about her being a big girl. Example: let her pick the vegetable for dinner...and tell her "wow, good choice..you're such a big girl, the baby can't do that." Well...good luck.