Is it permissible to complete the purchase of a house from a friend on an installment basis, knowing that she bought it with a usurious loan, and with the intention of repenting from accepting this contract?

It is forbidden to buy a house with an interest-bearing loan from a bank that does not own it, because it is a loan that yields a benefit to the lender. Nevertheless, whoever buys a house with an interest-bearing loan owns it legitimately and may benefit from it, despite incurring sin through usury. There is no harm in someone buying it from him. However, if the seller sold the house before owning it, this is not permissible in Islamic law, and the contract must be re-executed after she has taken possession of the house.