Is one sinful for helping his girlfriend apply for a job in a mixed-gender environment—like a hospital—due to the mixing that occurs therein?

It is permissible for a Muslim woman to guide her female colleague to a permissible job, and for this, she will receive the reward for facilitating benefit to others. It is also permissible to guide her to beneficial educational courses, provided that it is highly probable she will adhere to the Sharia-compliant regulations in mixed-gender environments. However, if she knows or it is highly probable that she will not adhere to them, she should not guide her.