Is it permissible for a girl studying at a distant institute, who finds it difficult to perform ablution in a covered place, to perform tayammum?

Prayer is a great matter, and it must be preserved and performed on time. It is not permissible to perform tayammum (definition) (dry ablution) when water is available and one is able to use it, because Allah does not accept the prayer of one who is in a state of impurity until he performs wudu (ablution with water). Tayammum is only prescribed when water is not available or when there is fear of harm from using it. Therefore, tayammum is not permissible when one is able to use water, and wudu can be performed inside the restroom.