I don’t like her romantically and want nothing sexual with her either. She acts desperate to talk to me, won’t get into more details.

I could act busy each time she approaches me, and avoid her as much as I can but I don’t know if I should tell my manager about this. I don’t even know what I’d tell a manager: “I’m informing that I want nothing to do with X and I’m going to keep my conversations with her to a minimum”?

Another idea: be boring as f*ck.

Do I tell her friends I don’t like her?

Ideally I could tell her directly I’m not interested / I don’t befriend coworkers (not true but it would work to soften the blow), but I simply don’t know how defensive she’s gonna get, laugh it off or accuse me of playing games.