While getting more women interested in natural science and tech is an important issue, the current approach in the States isn't working, and one of the major point in you-know-what is that despite the aggressive, well-intentioned push of female representation in traditional male dominated industries in fictional media(it does go too far sometimes), it does not seem to translate into the real world, ans enforcing a female only job fair also seems also well intentioned but unhelpful, because ultimately, you can't force people to like something.
It's troubling, but there doesn't seem to be an easy solution to this.
Oftentimes what these events actually are for is more about solidarity than recruitment. One of the issues with male dominated fields is that oftentimes they are exhausting to participate in when you are treated as an outsider. Having a community space where people can get together and talk shop, ask frank questions about culture from recruiters and gather strength from visibly seeing other people doing the same thing you do can give a sense of not being so alone.
That and a lot of women require a lot more data on how they compare before they feel like they are actually a viable candidate. They are sort of trained into an almost crippling idea of modesty and more social anxiety in general so a lot of them will only apply if they solidly fit the listed requirements. When they utilize a dialogue based recruitment space they can gain confidence that small missing bits of listed experience desired on their resume don't fully discount them from being a candidate for a job and gets more of them to apply. Women lean on pack tactics more than men do so these sort of events actually fufill a lot of secondary objectives than just on the day hiring.