Is it necessary to change sanitary pads soiled with vaginal discharge before performing ablution (wudu'), and is it necessary to ensure there are no discharges in the vulva before performing ablution, knowing that these discharges and gases increase during prayer times?

These secretions, known as vaginal moisture, are pure according to the most preponderant opinion, but they invalidate ablution. They do not defile clothes, and only ablution is required because of them. If their discharge is continuous, such that you do not find enough time for purification and prayer, then perform ablution after the time for prayer begins, and pray as much as you wish until that time expires. The questioner may also be afflicted with waswasah (whispers/obsessive thoughts), and in this case, she should ignore these whispers and turn away from them.