Is it forbidden to communicate via messages with a girl with the intention of stipulating her full adherence to Islamic law, and asking her to wait for marriage with certain conditions, for fear of losing her, knowing her academic excellence?

The trial of women is great, and the Prophetic Sunnah has warned against it. Therefore, Islamic law has established a strong barrier for a man's interaction with a non-mahram woman, such as the hijab and lowering the gaze. Speaking directly or writing to a non-mahram woman is not permissible except out of necessity, and only to the extent of that necessity, while adhering to the Sharia guidelines. If you are safe from temptation, it is permissible; otherwise, it is obligatory to avoid it.