When my twin girls were 3.5, they knew how to potty and were just refusing to do it all the time. For one of them, it was definitely that she would forget while she was busy playing etc. Here is what I did, and I got this from reading suggestions from this list, although I slightly modified it. I took the girls to the store and let them pick out a really special toy - in their case, they picked Care Bears. I told them that we were going to get those toys to use whenever they successfully used the potty - in their case it was just pooping that they had problms with. So I called the new bears their "Poopy Bears," and made the rule very clearly that when they used the potty to go poopy, they would get to play with the poopy bear, and when they did not the bear returned to the shelf in the closet until success was reached again. It was never negative; it was just the nature of the bear. I never chastised or showed displeasure when they had an accident. If they were upset that the bear was taken away, I would offer positive encouragement - "Yes, I know it's sad that the poopy bear has to go back in the closet, but you are a very big girl and I know you will be able to go poopy in the potty real soon." They would then work really hard to go potty again so they could get their bears back. For me, that worked well. They were very competitive and they liked being able to work towards a goal. It might work for you because it will give you something to tune into your older child - a little extra attention showered when she gets the rewards - to distract her from the loss of attention attributable to the new baby. Try also to involve her in "helping" you with the baby as much as you can stand; it will make her feel more involved and more secure. Find some time to have special mommy time for your 4 yr old on a regular basis - even if it's just 5 minutes, it's more the routine and the regularity of the time that makes an impression than the length of time. Good luck!