Can I tell a nine year old the truth?

I am going through a hard moment right now. My niece and I are very close. I been there since day one and if I could raise her as my child I would in a heart beat. My brother stopped paying full child support because he doesn't have a job. My ex sis in law has taken my niece for ransom and she said we are not going to see her until he pays. We already have motions but we are waiting for the court order which takes some time. I was wondering if is safe for my niece to know at this age why we haven't seen her or talked to her for so long.