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.
It sounds like your inferring a lot in this. Maybe she’s just kind and has a flirtatious personality. If she’s just being overly nice and you think she’s coming on to you, just don’t reciprocate and live your life until it comes to a head. None of the details you’ve provided are enough for anyone to know your situation well enough to know whether or not she’s into you. It’s very possible she likes your company, conversation, or just enjoys being around you. That’s just normal behaviour for someone that enjoys someone else.
If she’s makes physical advances or makes statements that are inappropriate, then you have something that you can respond to, politely, to defuse the situation and clear the air. Don’t lead her on and be flirty yourself. It’s possible you have an addictive personality that you’re unaware is affecting her.
DO NOT TALK TO HER FRIENDS ABOUT THIS! That is easily one of the dumbest things you can do. How do you think that would play out? I wouldn’t talk to a supervisor for a similar reason. If she starts crossing lines or getting damn close, then have a civil conversation with her.
Just live your life, and cross that bridge when it’s an issue. It more sounds like you’re annoyed by her. If you enjoy her company, then don’t burn that bridge by doing something dumb.