Loan to sister is unpaid

[bob107]

From about 1994 until 2000 I loaned my sister about $60K for college and law school expenses. She paid back about $15k from 1998 to 2001 and refuses to pay the rest. I have her initials on my credit card bills denoting which expenses were hers and some handwritten notes from her regarding payments she made. Our father has tried to negotiate this between us and can verify my loan to her, though he is understandably reluctant to do so. Can I compell him to testify agianst her? What legal channels are available to me to get paid? Is there a statute of limitations? Thanks.