If XYZ university is able to transfer the sevis record, your sister will be all set to study at abc university. Also, you need to request a sevis release form from abc university and ask xyz university to sign it and submit back to abc university. Talk with xyz university and tell the current situation, and they might able to do it for your sister. Good Luck. I had the similar situation long time back, But, I stayed with xyz university at the end. :)