Andrea, could you have planned this any better? :D
moving to a new home is such a terrific opportunity to make change in your life & in your family routine!
when my husband & i moved, we took the opportunity to have our son say goodbye to the old house... we took him through after everything was cleaned out... then we introduced him to the new house. we had set up his bedroom ahead of time. we added a couple of new wall hangings & made sure he knew all his old favorite stuff was now in the new place.
he really felt so grown up! we had already transitioned him to his toddler bed before we moved, but at the new place, we raised his bed frame significantly higher from the ground. he loved his "big boy bed". we had put new character sheets on his bed too. he embraced the change!
if your little girl has a favorite character or animal, you might consider investing in some new sheets for her "big girl bed". maybe a wall hanging, or some kind of decoration. she knows she will be a big sister soon & you might just tell her how important it is that she "gets" a new bed!
i would certainly recommend you start right from the beginning the first night in your new home. your little girl will be transitioning just as you will be. i think it will be easier for her to adjust to a couple of changes at once rather than: adjust to new home, then new bed, then new baby, etc. you could connect the two first relatively simple changes in environment.
most important: you know your daughter best. you will make the healthiest choice for her & for you.