How to prepare toddler for new baby??

I need advice or a book to help my toddler prepare to becoming a big sister! We just moved into a new house and it's still unorganized due to renovations still going on! But the past few days my little girl has been horrible with potty training! She's almost 3 and has been doing so good. But she has peed and pooped in her pants lately and just crying throwing fits and being horrible lately! Crying for new toys. It's been pretty stressful! I need any advice!!!