It's difficult. We get it in electronics all the time - At uni 98% of our electronics degree course were male, typically white or Asian. After 17 years in electronics, I have still only met 1 female working as an electronic design engineer.
This is more of a problem with aspiration, girls in the 1990s didn't want to do engineering/comp sci because it was a dorky/messy thing to do. Guys kinda just learnt it arsing around trying to fix their cars/pirate music and 'specialist media' on the interweb. So err, we are in that annoying situation where girls didn't want to do maths/sci 'cause it was hard and icky', but want the same salary doing flexible part-time work in a 9-5 clean office environment in their hometown? Hmmm, difficult. They are perfectly capable of doing it - but lack of take-up and experience is holding them back.
PS The female engineer I did meet was a total ninja/nerd and massively better at her job than me...it was great. Before that we pretended an old engineer with a pony tail was our romantic ambition.