Is it commendable to perform ghusl immediately after intercourse, and does not performing ghusl immediately lead to jinn hovering around the woman, preventing her from leaving her bedroom, and disallowing her from touching food?

All praise is due to Allah, and may peace and blessings be upon His Messenger, his family, and his companions.

The basic principle regarding the water used for ablution (wudu') or ritual purification (ghusl) is that it is pure and purifying, regardless of whether it is little or much, as long as it has not been affected by an impurity that changes its color, smell, or taste.

As for the water that has been used for purification, meaning the water that falls from the limbs during ablution or ghusl, it is pure, but it is not purifying according to the most correct opinion of the scholars. This is because the Prophet (peace and blessings be upon him) and his companions did not habitually collect it to purify themselves with it. If it were purifying, they would have done so.

However, if it is mixed with other water, then the ruling depends on the dominant characteristic. If the used water is little and is mixed with a large quantity of pure water, then it is pure and purifying, because the dominant characteristic is the pure water. But if the used water is large in quantity and is mixed with a small quantity of pure water, then it is pure but not purifying.

Based on this, if the water in the tank is abundant and the water falling from the limbs during ghusl is little in comparison, then the water in the tank is pure and purifying. There is no harm in performing ghusl with it. But if the water in the tank is little and the water falling from the limbs is abundant, then the water in the tank is pure but not purifying. In this case, ghusl should not be performed with it.

And Allah knows best.