I'm gonna go off on a little tangent here, and talk about this concept - because it seems very common among those who aren't successful when they come clean about this stuff, and they don't seem to understand why. This may be different for you, OP, because it sounds like you played it pretty well, and she is now pushing for a relationship with you. This is moreso for guys who think pushing for a relationship with them is effective - only to fail over and over. So, its a little different, but runs under the same concept. But possibly, if you continue down the same path, and assume her words to be facts - the same problem could apply to you as well. Who knows... Maybe its relevant for you also. Probably too early to tell at this point.
This ties in with the whole not revealing or admitting your entire interest too soon - because doing so has the opposite results of what you'd like. It most often will kill their attraction towards you. Its not what they say, or what you assume that's important - its what they respond to.
So, they might SAY you're lack of genuine interest is bothering them, but they're SHOWING that it raises their interest. Actions over words. Even though they may genuinely be bothered by it, and THINK they want to know - once they find out the truth that you like them, and want them for more than just sex (or whatever the case may be) - their interest plummets. It does bother them, true, but it intrigues them all the same. This is the ****ed up nature of attraction vs logic.
She doesn't want to be used for sex, or so she claims, but she's showing strong signs of genuine interest when that's all you are using her for - or that which she perceives to be the case. Whereas, if you came out and pushed for a relationship right away - she wouldn't want one, or push for one with you. Much like how she wants you to be nice when you are acting like a jerk, but avoids you when you actually are nice (especially to start off with). Or, when she starts chasing you after you lose interest in her. What are they RESPONDING to? That's what matters.
This goes back to the whole nice guy vs jerk dilemma. She might say she hates that the jerk doesn't care, but keeps going back to and chasing after him for the same reasons - constantly trying to win him over, and get him TO care - only to repeat the same process over and over. Meanwhile, the nice guy who assumes that what she claims to want is what she responds to acts on this belief, and is thereby rejected or friend-zoned - because he DOES care. It's too easy; she already knows he likes her; there's no challenge, or anything to win over.
This can confuse some people and make the girls seem like indecisive, double-speaking idiots - when they do and say these things at the same time - but its just attraction (or lack thereof) at work. I see it happen all the time, and experienced it a lot back in the day. These girls would piss and moan about not knowing where you stand, assuming you only wanted them for sex, and were practically obsessing over it / dying to know your intentions - only to lose interest once you came clean, and admitted to your interest. You could be the same jerk and nice guy listed above (at different times), and the results would still be the same for each scenerio.
I've had several instances of this that immediately come to mind. These girls would literally complain that such and such doesn't care - only to turn around and say "yeah, but you already like me" - as if to say that's a bad thing. Guess who they went back to over and over? Yeah, not me. They avoided me like a plague. Everything they claimed to want wasn't what they responded to - because I gave it all away too freely. The affection they wanted? Yeah, they couldn't run faster away from it. The interest, love, care, availability... Same thing.
People want what they can't have - from the people they can't get it FROM. That's what increases its value. The actual thing they want holds no inherit value in itself... None whatsoever. But when they can't get it from someone - oh yeah... In this case, they want a relationship because they think you only want them for sex. Now they are challenged and intrigued.
Always remember that when someone is bothered by something - it means they care about it. If they care about it - they're attracted to it. So, her saying you only want her for sex AS she's pushing for a relationship means she is responding to your lack of genuine interest, and pushing for a relationship with you - when you are only using her for sex. See how that works, fellas?
It's best to just keep your mouth shut, and keep them guessing for a while. Don't assume they will want you even more if you admit to your interest - because they probably won't. Challenge and unpredictability is pretty huge in the early stages of attraction. They do like to not know - even if they think or claim the opposite.
This applies to men, as well. How many of us chased after the confusing ***** who didn't care - only to complain about her, and avoid the nice girl who did care and was interested? It's just the way attraction works. So, no need to become angry or bitter over these kind of revelations; thinking all women are lying *****s who want to be treated like ****, etc.