Our 17 year old granddaughter was kicked out of her home, and sent to live with us. She arrived with only a suitcase of clothes. Her parents refuse to send her belongings, or to support her in any way, including giving us guardianship or custody. Can they be forced to at least send her personal belongings to her?

No. Unless she has reciepts for it they really aren't "her" personal belongings. As far as guardianship goes you could go to court to apply for it and ask for child support as relief.