Peace be upon you. According to Grand Ayatollah Khamenei (may Allah protect him): If there is certainty that no foreign man will see her, then there is no objection to it. Otherwise, it is not permissible, and it is the responsibility of the individual to determine this. According to Grand Ayatollah Sistani (may Allah protect him): If she knows that a foreign man can see her, it is not permissible for her to uncover herself, whether in the pool or elsewhere. However, if she is not aware of any foreign man seeing her, then there is no objection. May you be successful in all good.