There were lots of engineering schools that simply didn't admit women. The prevailing thinking at the time was that women were going to stay at home and raise kids. So there was no point in investing in their education. Further back in time, early pioneer women scientists had to marry scientists so they could work in their labs and only published under their husband's name. There are still vestiges of that attitude today as well as there not being a critical mass of role models that would make women being scientists and engineers seem normal.
Conventions are very difficult to change.
They permeate society. Mentoring is a strategy that is very helpful in encouraging women to stay the course and stick with engineering and science. The nature and impact depends on the individual. They are getting information they didn't otherwise have. They are getting advice, encouragement and support.