I've long been a fan of Lady Ada Augusta Lovelace. She was not only one of Charles Babbage's biggest patrons, but she also was one of the first to suggest the use of "Jacquard Loom" type cards as a way of programming the Analytical Engine as well providing what may have been the first software programs. Lovelace, the daughter of the infamous poet Lord Byron, was also herself a "free spirit", albeit one with an astonishingly brilliant intellect behind it.
Today (March 24), in honor of the Patron Goddess (or Patron Saint, as appropriate) of programmers, has been designated Ada Lovelace day. It is a day to recognize women in programming, and I find that, in working with the XML community, that there are a number of highly intelligent, technologically passionate and hard-working women in this particular field that more than deserve to be recognized. I present this list with no particular ordering in mind - these are people I have worked with or corresponded with, and I don't think the concept of ranking really applies here - they have all pushed the boundaries of XML in their own unique ways.
Dr. Jeni Tennison has been one of the people who's worked hardest to push XSLT in particular. She's written books on the subject (including one for O'Reilly), has spoken extensively on XSLT (and other W3C technologies) at conferences, has been one of the enduring presences in the xml and xslt lists and was the prime mover and shaker with the EXSLT.org movement, which laid the groundwork for many of the changes that ended up in XSLT 2.0. She's also worked on XML schema standards for ISO and more recently has been involved in the XQuery community, and I fully anticipate that she will continue being a major promoter for these technologies.
I would normally list people separately, but B. Tommie Usden and Deborah A. Lapeyre have been involved together in so many XML initiatives that people tend to assume they're just different aspects of the same person. Both have been the major organizers behind the XML Extreme conferences (which was, as of last year, rechristened Balisage), and both have been instrumental in making Mulberry Technologies one of the foremost XML consulting firms in the world.
Lauren Wood has worked with XML from its inception, including serving as Chair of the W3C DOM working group from its inception until 2001, laying down many of the pieces of that critical standard, serving as Senior Technical Program Manager at Sun Microsystems until January 2009, and being the Chair for the XML Conference Series from 2001 to 2005 (as well as serving on Balisage's advisory board among many others). She's also one of the most dignified and honorable people that I've personally had the privilege of meeting (Tim Bray, her husband and another of XML's pioneers, is another).
Eve Maler's first blog post in 2004 was entitled Ripping the X Off Her Varsity Sweater, and those times I have met her only serve to highlight both her fierce intellect and willingness to walk different paths than the rest of us. Eve helped with the inception of XML itself, and has additionally helped flesh out SAML, DocBook, the Universal Business Language (UBL) and helped get both Project Concordia and the Liberty Alliance off the ground. Her work in authentication and identity management has been seminal, laying the foundation for establishing presence on the web.
Priscilla Walmsley has been added here by multiple (well-deserved) calls by her many colleagues. Priscilla is the Managing Director of Datypic, an XML consultancy, was a key member of the W3C Schema Working Group, and coauthored both the Definitive XML Schema (for Prentice Hall) and XQuery for O'Reilly, the latter of which I have purchased four times now (once for myself and the others for clients to use as a textbook on how to work with XQuery). She also wrote XML in Office 2003 with SGML legend Charles Goldfarb.
This is not meant as a comprehensive list - indeed, I would love to be able to add your suggestions as to those women in the XML community that you feel have helped build the foundations of both technology and community and should be recognized for their efforts.