Must the prayer be made up if menstruation continued for 14 days, of which 6 days wereSpotting (Kudrah) and 8 days were blood, given that the usual duration of her period is 6 or 7 days?

The blood you saw is menstruation as long as it appeared within a period suitable for menstruation and did not exceed 15 days. Discolored discharge (Al-Kudrah) is considered menstruation if it is continuous with the blood or occurs during the usual period of menstruation. If the discolored discharge is not menstruation (e.g., if it occurs outside the usual period and is not continuous with the blood), then you must make up the missed prayers. If it is menstruation, then you are not required to make up the prayers.