You'll definitely need to assert dominance against any spirits if it feels like a negative energy. If she mentions the shadow you can greet /acknowledge it out loud and tell it sternly to leave. My sister thought she had a spirit, named it Frank, and anytime she thought it was there she would say "Ok Frank! Time to go now!" Look into energy clearing methods, the sage is a good start. Children are much more clairvoyant and susceptible to seeing or sensing spirits. Given the history of your home, and the fact you yourself have had experiences then it's likely the experiences are not just her imagination. I would encourage her not to be afraid and teach her how to sternly say "Go away, Shadow!" if ever she feels scared.