How about a "My parents arranged a marriage for me, even though they knew I wasn't interested. Said I had a responsibility to have children. I snuck out that night; last time I ever spoke to them." type situation?
That'd be the way that I'd want any direct mention of her sexuality - she's giving a brief summary of what her brand of crazy/adorable is (I mean she IS a BioWare character, that's in the job description), when she does the back story bit, it comes up like that, and there's no further comment on the matter. Maybe, if a male Inquisitor flirts with her, she says explicitly 'I'm not interested in men.'
But yeah, none of the 'I had a bad experience with men, I'm only with women now.' There's a large portion of men who wouldn't take that as a no but as a challenge.