Answer:
Bonnie means 'nice looking' or 'pleasing on the eye'. A Brae is an upward slope or the rise up to the top of a hill.
Loch Lomond has 'bonnie banks' as in the song.
A man could describe a woman he finds nice looking as 'bonnie'.
Woman in the early 18th century found Bonnie Prince Charlie 'good to look at'.
A new born child could be described as 'a bonnie bairn'. Bairn means child.