Hi, M.. My 2 and 1/2 year old daughter did a similar thing when my 4-month old son was born. In fact, the 2nd night we were home from the hospital, she went into his room, squtted on the floor, and peed! (LOL b/c you have to!) She also would pee while sitting on the couch next to me while I nursed her brother. I talked to my pediatrician, who did not recommend putting her back into diapers, b/c it would reinforce the regression. Instead, I made sure I was spending enough one-on-one time with my daughter so that she was getting the attention she needed. THink about it: what better way to get mom or dad's attention than to wet your pants and need help getting cleaned up? So, my husband and I implemented alone time with our daughter, which helped a lot. Along the same lines, we stopped giving her so much attention when she wet her pants. We would tell her, "Oh, too bad. We do that in the potty, not on the floor. Go get yourself cleaned up, please." She would have to get her own clothes off, wipe herself up, help clean up the urine, wash her hands, and get clean clothes on. Once she was doing more of this on her own, it became way less fun to wet her pants. We also reminded her of all the things she could do that her baby brother can't (like eat ice cream!) and how happy we were that she is who she is and not a baby. And, lastly, we reimplemented a sticker chart, which helped some, but not as much as making sure she was getting attention. Now my daughter goes on her own 100% of the time, and is even staying dry through most nights. Hope this all helps. Good luck! Your daughter will get there, too!