I'd have a pretty tough time saying that Jennifer Batten, Bonnie Raitt, Kaki King, Ani Difranco or any of the guitarists from 7 Year B*tch or Bottom don't (/a very unfortunate didn't) take their instrument seriously.

As do a number of women who I know from various local scenes.

I think there's a couple of different things going on here:

1). Guitar is a very male-dominated instrument and I think the issues associated with that tend to put a lot of otherwise serious female guitarists off.

2). Most women seem to care a lot less about technical, fast, mastubatory solos than men do. I think most women are more concerned with the song; the chord progression, the melody, rhythm, and lyrics. So, in other words, we're less likely to hear about their exploits unless they happen to front the band as well.