Straight friend is always flirting with me?

Ok, so I'm a bisexual 15-year-old. I came out to my friends back in September and they immediately accepted me because we're a very accepting group of friends, about most things. They've all been completely fine with it and not really put any emphasis on it. However, I do have this one friend who now seems to think it is ok to flirt with me. I don't know if I'm overreacting or not.
She is the biggest flirt out of our whole group, and flirts with everyone all the time, even though she has a boyfriend. This is really harmless flirting, she would never cheat or really take the flirting seriously, it's just kind of something she joes. Also, we're a pretty flirtatious group in general, at least with each other. We always joke about having sex with each other, we'll occasionally hold hands, and agree to be each other's girlfriends even though of course it wouldn't actually happen. We basically take all of that pretty lightly since none of us, except the one who always flirts with me, have boyfriends (or girlfriends in my case) or are likely to get one anytime soon.
So I guess I shouldn't really take her flirting too seriously, but I do feel like it's targeted at me particularly. If this is her way of accepting my sexuality then I don't mind, but I do feel like it's been an awfully long time since September and she's still doing it. At the beginning it was worse, she would ask things like "what would you say if I asked you out", which is a really difficult question for me to answer obviously, because I would always say no and she would be like "whyyyy, why don't you want to go out with me, I'm really sad now". Now it's not as bad as that, other members of my friendship group kind of stepped in and were like "look, it's unfair to ask that and you probably shouldn't", so I'm glad for that.
But now, for example, we'll be in a lesson and she'll just say, in front of the entire class "where's my girlfriend?" referring to me. I am not out to my school, and I don't mind joking about it because everyone will assume I'm not serious, but I feel like maybe it will make it harder for me to be serious if I do decide to come out to the school. She will also always hug me from behind, or cuddle me and put her face really near to mine. Of course when this happens, as well as feeling uncomfortable, I partly enjoy it because she just does it so often and it makes me feel close to her. I wish she wouldn't, because although I don't have feelings for her, I get closer to every time she does something like that. To be honest it could also be her just trying to figure out her own sexual preference, because before I came out I don't think most of my friends had given it that much thought, they all seemed fairly certain they were straight, but afterwards more of them started to wonder if they might be bi, or at least say they did.
I guess it just makes me feel uncomfortable because I feel like she does this more to me than to any of us, and me being the only non-straight one is obviously an influencing factor in this. Am I overreacting, or is it really too much?

I'm sorry for how long this post is :/

 

Thanks for the replies
Yeah, I'm sure that nobody else at our school really thinks anything of it, I just don't feel that comfortable with it. She does flirt with some of my friends, but in less of a touchy-feely way, she'll just go "oh yeah, [friend] and I had sex last night, didn't we". With me it's more like she's constantly trying to be as close as possible to me, or just trying to make me feel uncomfortable in general. And the problem is that the more she does it, the more I enjoy it haha.

I don't feel like I really can talk to her about it, though, because she'll probably just think I'm overreacting and I don't really want to make a big thing out of it, because I don't know if I am overreacting or not. I guess I probably am.

 

Yeah, that's probably a good idea actually haha...
Thank you for the help