Bass over guitar
Judging from a purely eye-candy point of view, more hot female bassists than female guitarists.
(Ghost Atreides enjoying incontestable health benefits on, Mon 28 Dec 2009, 1:02, 1 reply)

Are you using
Suzi Quattro as a reference there?
( sandettie light vessel automatic New Twitter - @bollocksreally, Mon 28 Dec 2009, 1:03, closed)

As well as Quattro, I'm using the following as a reference
In no particular order:

Paz Lenchantin
Emma Anzai
Jennifer Arroyo
Sheryl Crow (plays bass as well as guitar, natch!)
Melissa Auf der Maur
D'Arcy Wretzky
Lyn-Z (Mindless Self Indulgence's bassist) (despite getting nobbed by that bloke from My Chemical Romance)
Nikki Monninger
Elena Jane

You can have the female guitarists, I'll take the female bassists.
(Ghost Atreides enjoying incontestable health benefits on, Mon 28 Dec 2009, 1:12, closed)

I would like to add
Elena Jane, the former bassist from End Of Level Boss. She knows how to rock the fuck out and is hot as hell. During Googling to find a picture I also found that the Metal Hammer staff think the same.
(cypherspace is not a toaster, Mon 28 Dec 2009, 1:22, closed)

Oooh
*Adds her to the list of hotties*
(Ghost Atreides enjoying incontestable health benefits on, Mon 28 Dec 2009, 1:33, closed)

Kim Deal?
Before she got too friendly with Mr Brownstone?
(Sir Tainley Barking Ezekiel 23:20, Mon 28 Dec 2009, 16:35, closed)

Suzi Quattro, PJ Harvey and some bird with glasses on Later with the Joolsmeister using a Boss looper [edit:KT Tunstall, thanks to the internet]. Weirdly arousing.
(NiplyTheElder tried to slip clunge into a conversation on, Mon 28 Dec 2009, 1:13, closed)