How to give proper but polite hints to reject someone?

First of all, I just want to apologize if this offends anyone out there, but if I do, I absolutely don’t mean it.. I just need some help to solve the problem that I’m encountering right now.

I’m just wondering if anyone have been wooed or pursued by someone of the same sex, but you absolutely has no interest in that way at all (you are straight)?

I have a friend whom I originally thought was just a girl who’s rather tomboy. I didn’t realised that she’s actually into girls at all. And recently, I’ve got a strong feeling that she’s trying to pursue me by trying to ask me out, keeps texting me, and so on.. I’m just wondering how should I let her know (hints, etc.) that I’m straight, but in a very polite way?

Oh ya and I’m thinking that she’s this way because there was once when we were talking, and I said I don’t like pink color.. And she said “oh you’re a tomboy then?” and I said, “yes, I used to be a tomboy, but my mom told me to change”
I’m not sure if she has the wrong idea or not, but I thought tomboy means that a girl who dresses up and likes ungirly stuff.. which doesn’t necessarily mean that I once a lesbian (and I NEVER am).. So I’m just wondering if the context “tomboy” also means that you’re “lesbian”? or no?

And how do I give her hints that I’m not into girls at all (politely/indirectly)?

Thanks! and I really don’t mean to offend anyone out there.. I really don’t. But if I do, once again I sincerely apologized for that. I hope you understand. Thank you!