It almost certainly has to do with the fact that she has a new brother, but I am at a total loss as to how to deal with it.
If I ask a question, she'll either ignore it or answer with a noise that is somewhere in between yep and nope. If I ask her to do something she ignores it. If I tell her about something she tries to ignore it. The only conversation that is possible is via teddies.
I have tried- Ignoring her Speaking loudly like English isn't her first language and somehow if I'm louder she'll understand me better Talking to her about the importance of listening Punishment (withdrawing fun things like going to the park)
Unsurprisingly, none of these crap ideas are working. There are other issues surrounding the upheaval caused by a new sibling which, I think, we are dealing with. But this issue makes our days so difficult- it becomes so hard to have a meal, go outside, play in the house-that I just give up and turn the TV on.
I don't really know what to suggest but didn't want to leave you unanswered. We've got this problem on a smaller scale with DS (3.7), in that he listens sometimes, but other times it's like talking to the wall. His problem is distraction or boredom usually.
Is your DD still getting one to one time with you? Do you get her involved with things to do with the baby?
DS1 never listens and it drives me crazy!! So i count: 1, 2, 3 before removing the toy he is playing with... sometimes it works, other it doesnt. If it doesnt then i tell him again what is going to happen and count again and usually he will do it. and of course i lecture him at least twice a day about listening to mummy and daddy... I hope that is just a stage and that he will grow out of it very soon!!