While Stella Was in Hong Kong, a Loan Came Due

While Stella was in Hong Kong, a loan came due that she had guaranteed. The creditor, a kindly old man, extended the due date on the loan for thirty days, interest free. Did this action by the creditor discharge Stella from her obligation?

A) Yes, since Stella was not consulted on this change.
B) Yes, because consent by Stella would be required.
C) Yes, since her position as a guarantor was clearly prejudiced.
D) No, since the change is obviously to the benefit of the guarantor.
E) No, because the risk is not materially altered to her detriment.