Unfortunately it is completely normal for big changes such as having a sibling to cause a regression. Hopefully won't last long. My oldest 5 in 2 weeks still has accidents when big changes happen although less now accidents now. My youngest has started having lots of accidents since my oldest went to school, nursery bribed him and he's having way less, he's obsessed with bin lorries and they bought bin lorry stickers and everytime he uses the toilet he gets one haha. He's had a couple of days with no accidents at all. So bribery can definitely help, whatever works for your daughter 😀
Exactly the same happened to us! Our three year old regressed when her baby brother was born. We were suddenly having accidents (seemed like out of choice, wanting to be changed etc etc), and we just had to keep reminding her and she did come out the other side after a month or so. It is very common I think. We really struggled with poos, she was withholding and giving herself a stomach ache, no appetite etc, so (rightly or wrongly) we made it into a positive experience by saying if she sat on the toilet she could watched her tablet whilst she did a poo. It worked instantly, and she has done a poo every day from then on, she only wanted the tablet for a week or so, now she just goes and sits on the toilet herself and will just chat to herself.
We used a potty training chart, pull ups then training pants. We didn’t use food as bribery, but did a lot of celebrating when our little one used the potty and once they got so many stars on the chart we bought them a small toy, so 100% used bribery 😂 We talked a lot about toilet habits, and she came with us when we went to the toilet. For a few weeks, our little one was afraid of doing 💩on the toilet but we did a lot of positive talking around this, and lots of excitement when she eventually did this. She started training pants in July this year our little one is completely toilet trained now, independently uses the bathroom (apart from help with wiping) and has full understanding of tap use / temperature control etc. Potty Training is not fun at all, (in our opinion) one of the worse hurdles. All children are different and will do things in their own time. You are doing a great job ❤️ Try not to stress and things like “Pooland” on YouTube helped us aswell ❤️