In 2008 Lee Munroe found at least 25 female webdesigners he found worth to be mentioned http://www.leemunroe.com/25-hot-female-web-designers.

Already in 2010, smashing magazine published a small list of female webdesigners:  http://www.smashingmagazine.com/2010/05/11/women-in-web-design-group-interview/.

Is it important if webdesign is female or male?
Later, in 2012 another article in Templatemonster takes a look at the design: http://blog.templatemonster.com/2012/07/26/web-design-by-gender-women/ and the different styles preferred by gender separation.