My daughter is 3.5 and was doing really well, but has been really regressing for about a week. She was/has been sick, as has her little brother. We were out of town for a couple of days prior to that. But for the past week she has been regularly either: failing to make it in time to the potty or completely blowing it off and just going in her pants (both). She has told us on a few occasions but typically just sits in the poo or will take off her underwear and leggings for pee and will try to cover up/clean up the pee. I have found evidence for both. We have tried not reacting and just cleaning her up and emphasizing that big girls go in the potty (what her teachers at school do, as she has had several accidents there last week and already today). We've also tried punishing her/getting upset. Neither seem to have any lasting effect as she will have 1 good day and revert the next. Or a good morning and bad afternoon. She stays dry overnight and makes it to the toilet in the morning. I think she does this sometimes because she doesn't want to stop what she's doing and go, and I realize that we need to make her go more regularly. But several times, including this morning at school, she has gone pee on the toilet and then 10-20 minutes later has a BM in her underwear. (She can do that at school in front of her friends!) I'm not really sure what is developmentally appropriate at this point, though I know we need to be consistent. She has made comments to her teachers about her 13 month old brother being in diapers, but also being a big boy now (not a baby). We started rewarding her again for going in the toilet, but apparently that doesn't have a lasting effect. Is it possible that it's a physical/medical issue if she only does it part of the time? Or are we really dealing with a behavioral/adjustment to new house/school/little brother getting bigger/mom & dad being busy? It's getting old!! (history: we moved in July when she was 3 years 3 months and she was potty trained right after we got here. So, the adjustment is recent as is her potty training.) Thanks so much!
Regression like this is common at that age. It could be related to your younger child, it could be nothing more than not wanting to take the time.
First, since she was recently sick, I would have her checked to make sure there isn't a bladder infection, or something.
Second, I would see what the school schedule is. It could be that she is asking to go to but that the teachers are telling her to wait until lunch, or storytime is over, and she can't.
Third, ask her. Tell her that brother is going to need her help in getting out of diapers. What are some things that will help him not mess his pants?