M daughter is 12 islamically 13 and wears hijab. Can she take swimming lessons with a female instructor? If there are men sitting outside of pool is it allowed? If some men but they are busy with their children or are elderly in the pool and are on another side of the pool can she take these lessons or go in to swim? I feel bad that her brothers are allowed but she isn’t. Are there other options for her to go swimming in the summer? She has a hijabi swimsuit that is loose and also swim shoes to cover her feet.

From Ayatollah Sistanis site:

Question: What is the Islamic opinion to swimming in unisex environments such as the beach, swimming pools, and other areas?
Answer: It is not permissible.

So the only option would be women only gyms and swimming pools but even there sometimes the lifeguards and instructors are Male.