Your agreement with the pharmacist to open a pharmacy, whereby you supply the capital and she supplies the certification by means of which you can get the licence, in return for a specific monthly salary paid to her, seems to us to be permissible, on condition that those who work in the pharmacy are qualified and the salary that is paid to the pharmacist is in return for getting the licence in her name. This is a real benefit for which one may pay money.
What is problematic is giving the work in the pharmacy to people who are not qualified, which means that they will be ignorant about medicines and mixing them, and this will cause harm to people.
For a woman to work with men in the same place is something that usually leads to negative consequences and problems, even if she wears hijab. Men are naturally attracted to women, and women are naturally attracted to men; if they spend a great deal of time together, that may lead to familiarity and leniency with regard to looking and talking. They may end up being alone together and that may lead to more serious consequences. Hence Islam forbids mixing, and this is indicative of its perfection and dignity, and demonstrates that it is based on achieving what is in people's interests and warding off what is harmful.
Hence we advise you not to employ a woman in a place where she would mix with men.
And Allah knows best.
Reproduced from Islam QA