HUGE congratulations on your wonderful news
I had a 9 year old Border Collie when I gave birth to my first child. I had also owned a rescue Chow but I had to give her to my dad when I found out I was pregnant as a condition of her rehoming was that she was NOT to be around young children, she had bitten them in the past.
However, my collie was wonderful with my daughter and watched over her. We made sure that from about 3 months into the pregnancy we started laying down rules about where she slept (had previously slept in the bedroom) and we invited lots of friends with baby's over. We also put the moses basket in the lounge 3 weeks before the baby was due to get her used to the idea.
We made sure she had enough attention when we took our baby home and she was absolutely fine. Sadly we lost her a year later to cancer
Chances are Maggie will be fine with the baby. Lots of people panic but although dogs often become a bit jealous at first, it's very rare for a dog to harm a small baby.