What is the Ruling of Studying in Mixed Universities to give dawah?

So, we go back to the previous speech, She burns herself so that she can benefit others; She is committing prohibitions of the shari'ah; she has no excuse to commit these prohibited matter. That's because seeking knowledge in universities today, fundamentally, is not fardh ayn (an individual obligation) upon her, so that she can turn a blind eye to some matters that aren't considered as an individual obligation. At most, what could be said is that this can be a communal obligation; If some establish it, then the obligation of fulfilling it is taken off from others. However, with that, I think that there is more harm than benefit in what female students study in universities nowadays. So, how can this be taken as a means for doing da'wah to Islam?