Nine year old sharing bed

Lindsay 🌺

My niece is almost 9 years old and refuses to sleep in her own bed. Her parents are split and her father (my sisters not so fantastic ex) says that he won't push the issue, the child will sleep in her bed room when she feels ready. My sister is dying to have her room (and bed!) to herself. But with two completely different parenting strategies-how can my sister ever get my niece to sleep anywhere else??