My DD1 is 27 months now and has been fully TT day and night for five months now. She did go through a few periods where she would have accidents regularly but because I knew it was genuinely an accident we didn't make a big deal about it. I just made sure that I told her that wees are only for the potty/toilet. She did have one accident two weeks ago where she wet her pants but ran to me and told me. She'd held on after it started and finished off in the potty. I think it was because she had a friend over and they were so busy playing that she didn't realise she needed to go until it started happening. I've heard many people say that this is quite common. I wouldn't attribute it to your new bubba's impending arrival. Sure kids can sense something but I don't think it's that extreme. It could just be a phase. The great thing is, you know she can do it so just keep doing what you've been doing, stay consistent and she'll get back on track.

PS I'm assuming that by accident you mean wee and not poo.....good luck!!