All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It is not permissible for a Muslim to borrow money with Riba (interest or usury) whether it is a large or small amount unless he is in a dire necessity which could not be fulfilled except by resorting to this Riba. The necessity here is when a person is in a situation whereby if he does not consume what is forbidden he will die or be in an extreme hardship which is unbearable. Of course, the need to marry off your sister is not included in this necessity. For more benefit, please refer to Fataawa 82102 and 86701.
Allaah Knows best.