Is a second menstruation, one week after the first, considered menstruation, and does it obligate prayer and fasting, given that the duration of both menstrual periods may exceed 15 days, and she uses contraception and is 48 years old?

The minimum period of purity between two menstrual cycles has no limit. Whenever a woman experiences menstruation after her previous one, it is considered menses, whether the period was long or short. This is the view preferred by Sheikh Ibn Uthaymeen. A woman can also menstruate twice in a month, provided that the blood has the characteristics of menstrual blood. Similarly, the maximum duration of menstruation has no limit; whatever a woman habitually experiences as continuous bleeding is considered menses, even if it lasts seventeen days. However, continuous bleeding throughout the month, or bleeding that stops for only a short period, is not considered menses but rather irregular bleeding (istihadah (definition)).