Is it permissible to accompany a friend to look for a house she wants to buy with an interest-based loan, and to offer her an opinion on it?

Usury (riba) is unequivocally forbidden in Islamic law, whether a person takes it to buy a house or for any other purpose. The texts indicate its prohibition and curse those who consume it, feed it, write it, and witness it. It is not permissible to help your friend take usury, because a Muslim does not assist his brother in sin and aggression. Rather, it is obligatory for you to advise and guide her.