Is it considered haram for a girl to sleep sitting in a train in front of a strange man, knowing that she travels daily and returns late?

A woman is not permitted to travel except with a mahram (definition). When traveling, she must take precautions to avoid mixing with men as much as possible, and she must be fully covered by her clothing. She should also strive to get enough sleep before traveling to avoid anything from her being uncovered or men seeing her while she is asleep. If sleep overcomes her despite her efforts, then there is no blame upon her. The fundamental principle is that she should remain in her home unless there is a necessity, subject to the aforementioned regulations.