At 4 and a half your daughter is old enough to understand a heck of a lot about what will be happening. Tell her straight up. Talk to her about the sleeping arrangements. Maybe she'll even have a great idea? My 4 yr old would LOVE to plan anything related to a new baby sibling (poor kid will never get one though, lol).
My 19m old woke up every time my new baby did...even though he had slept in his own room upstairs his whole short life, and was a great sleeper too. The baby in the master bedroom downstairs was a new noise at night and he woke every time. There was nothing I could have done to prevent it. At first I went into his room and checked on him when I could hear him wake up, but it quickly became obvious that it wasn't necessary. He would wake up, move around a bit, didn't cry, and settled back to sleep. He napped a little more during the day to make up for it. He was too young to really understand any explanation. After a few weeks he slept through again.
Tell your daughter that babies wake up in the night, she'll probably hear it and wake up too, it's normal, she can stay in bed and you'll check on her when you are done feeding/changing the baby and everyone can go back to sleep. It might sound simplistic, but it the bigger deal you make of it, the bigger deal it will be. Maybe your daughter can make suggestions for things that will make it easier for her to stay in bed and go back to sleep. A new toy to hug (maybe it will be a present to her from the baby), a new nightlight, soft music she can turn on, new sheets, new pajamas, a special big sister cup on the night stand for that last drink of water.
If you want to experiment with different sleeping arrangements before the baby is born, go ahead, just include your daughter in making the plans. My son went through a stage of not wanting to go to bed knowing my husband and I were still up downstairs. He agreed to stay in bed quietly if one of us would go kiss him every 15 minutes. We put a clock in his room and would tell him where the hands would point the next time we'd come up. He was usually awake for only 1 or 2 extra kisses and that phase was fairly short lived. You could start practicing that with her now. Help her own the role of big sister and start a few of the "responsibilities" that will come with it.
You could reward her for every night she stays in bed without issue. A row of stickers to get an ice cream, a penny/nickle/dime/etc until she has $1 for a trip to the dollar store, etc.