First, no matter how she is acting, no matter that she's in spirit form, she is a child, and needs to be treated with love and understanding. She doesn't know why she is there. She's confused why mommy and daddy would up and leave her.
Have your friend light some white candles. Smudging the house can help if there is some attachment she needs to let go of. Call forth your guide and hers. Someone on the other side is waiting for this girl. Probably not her parents, but perhaps a grandparent/great grand parent/older relative or neighbor that will take her over. This little girl does not need to be afraid, there are children on the other side for her to play with.