Pete
The heads on the spikes belonged to characters who were travelling, if I recall correctly. A group of good guys was travelling from the fair in Kingdom to one of the other communities. The Whisperers intercepted them in route. Then the Highwaymen arrived and tried to rescue everyone, but there were too many Whisperers and they were captured and beheaded too.
?
She probably helped some of her soldiers sneak into the fair and quickly kidnap everyone during the movie.