Is it permissible for a married Muslim woman, who works in research and wears the hijab, to complete her PhD studies in a mixed-gender environment with non-Muslims in Canada? And what is the best advice regarding this?

There is no objection to a woman working or completing her studies as long as it does not lead to a forbidden شرعي (Shar'i) act, such as impermissible mixing (اختلاط محرم), seclusion with men (الخلوة بالرجال), fear of temptation in her religion (خشية الفتنة في الدين), or studying what is impermissible. If a forbidden شرعي (Shar'i) act is found, then preserving one's religion, obeying Allah, and fulfilling her duty as a wife and mother must take precedence over work and study, based on the Prophet's (peace be upon him) saying: "Indeed, you will not abandon anything for the sake of Allah, the Blessed and Exalted, except that Allah will give you something better than it."