Homophobia is when you discriminate against non-hetero people as friends, co-workers, employees, check-out clerks... In other words, relationships that have nothing to do with your own sexuality. But people are free to choose any and every restriction when it comes to who they date.
I am inclined to say that nyc's attitude is, indeed, prejudiced and discriminatory. I'm also inclined to say, so what? We all exercise discrimination when we date, or else we would all be dating every person we meet. I don't mean the usual ad homonym fallacy of using two definitions for discrimination. I mean we all reject some potential mates based on arbitrary criteria. Literally, we discriminate against them.
It just so happens that discrimination due to sexual orientation is a hot topic these days. But remember to keep it in context. It's not like she's saying she won't sit next to bisexuals at the movie theatre. She's saying that there's "something" about bisexuals that just makes her clit stop throbbing.
Long story short, no one has the right to tell anyone else who they must date. You can disagree with her preference 'til the cows come home, tell her she's got bad taste, tell her she's fickle, whatever. But I wouldn't call her homophobic, anymore than I would call a lesbian heterophobic if she won't sleep with bisexual women.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker