Whose faith is the subject of Hebrews 11:11?

Πίστει καὶ αὐτὴ Σάρρα δύναμιν εἰς καταβολὴν σπέρματος ἔλαβεν καὶ παρὰ καιρὸν ἡλικίας, ἐπεὶ πιστὸν ἡγήσατο τὸν ἐπαγγειλάμενον (Hebrews 11:11, Westcott and Hort) The traditional translation of Hebrews 11:11 implies that it was (at least...