Does one have to make up nineteen days of fasting after the cessation and intermittent return of menstruation during Ramadan, knowing that it usually does not exceed seven days and that she fasted most of these days?

Days are not considered menstruation if they exceed fifteen days and are not separated by thirteen days of purity. If you are experiencing irregular bleeding (istihada), then menstruation is the duration of your usual period or what you distinguish as menstrual blood; otherwise, it is six or seven days based on estimation. Your fasting is valid on non-menstrual days, and you do not need to make it up. However, your fasting on menstrual days must be made up. If you missed prayers during the days of irregular bleeding, you must make them up.