Is one ablution sufficient for the Maghrib and Isha prayers for a woman who became pure from menstruation at Isha, or for the Fajr and Dhuhr prayers for a woman who missed Fajr, knowing that she suffers from continuous flatulence and urinary incontinence?

The difference of opinion you alluded to regarding this issue is well-known and valid. However, what is held as authoritative by us is that a person with a continuous ritual impurity (hadath (definition) da'im) must perform ablution (wudu') for the time of each prayer. With this ablution, they may pray more than one obligatory prayer and as many missed prayers (fawa'it) or other prayers as they wish, as long as it is within the prayer's time and they have not incurred another impurity besides the continuous discharge. So, if you become pure from menstruation at the time of 'Isha, you pray Maghrib and 'Isha with one ablution. Similarly, if you missed the Fajr prayer and prayed it with Dhuhr, you would do so.