Find common interests and invite her to things not involving thesis papers. Compliment her in unexpected ways. Initiate some subtle touches to the shoulder/arm/hand region if she seems open enough.
If her friendliness increases, ask her out. If that fails, go for the old stand-by...
"Wow. I love your skirt. It'd look great dangling from the ceiling fan in my bedroom."
That line's always worked on me, after all.