How to get women to apply for theses and research projects requiring (rudimentary) programming skills?
Teach computation throughout the undergraduate curriculum.  All your students need to know it anyway.  Examples: https://www.compadre.org/PICUP/webdocs/About.cfm
Ensure all students know why your research is worthwhile.  If the cause of your problem is stereotypes, relating the work to students' values is a way to overcome that.
Educate your students about bias.
Inform your students about minority role models.  Don't know any?  Here's one https://research.seas.ucla.edu/carter/.
Develop a reputation for being a good mentor.

There are no magic instantaneous fixes.