What is the ruling on a woman performing tayammum when she is outside her home at the time of prayer and there is no water available in the mosque?

It is not permissible to perform tayammum (dry ablution) when water is available and one is able to use it. One must search for water, based on the Almighty's saying: "And if you find no water, then take for yourselves clean earth and wipe your faces and your hands with it." If water is available for sale at its usual price or with a slight increase, tayammum is not valid for someone who can afford to buy it. If she does not find water after searching, she may perform tayammum. However, if she can delay the prayer to perform ablution at home before the time expires, that is better.