The definition of sexual harassment is
EEOC wrote:
Unwelcome sexual advances, requests for sexual favors, and other verbal or physical conduct of a sexual nature constitutes sexual harassment when submission to or rejection of this conduct explicitly or implicitly affects an individual's employment, unreasonably interferes with an individual's work performance or creates an intimidating, hostile or offensive work environment.
The two keys that I see here are that the action must be unwelcome and it must adversely effect the work environment. It's also a federal law (part of the civil rights act of 1964), not a state thing... which means its consistent across the board (unlike age of consent, etc. etc. etc.). I'm not a lawyer or anything, but if she was so offended by your seemingly harmless actions that it negatively effected her work performance, wouldn't she have asked you to stop? She didn't even refuse your attempts ("No thank you, I already have a boyfriend."), she just put you off. I think you may have a case here.