Bless you for adopting Maggie, I hope you have many happy, healthy years together. She is lucky to have found you.
I agree with the above posters, give her time. In the meantime, though, it doesn't hurt to look into what it may take to curb some of her reactivity.
Start here, perhaps, there are a lot of resources on the web. I am sure you will, but try to stick with postive only methods and avoid corrections and flooding.
You're awesome to be helping her! Thank you! and Best wishes!!
Canine University: News -- Canine Behavior - So Your Dog Is Reactive!