She's clingy, immature, and insecure. Not a good combo! Look, here's the deal (and why a lot of guys once they're a bit older don't want to sleep with virgins). A lot of girls have these fantasies that they'll find "the ONE" and they DO say it with that emphasis on "one". And then life will be perfect, he'll be devoted to her, blah, blah, blah.
It's an adolescent dream, and then when they finally decide "go all the way" some trigger goes off and the guy becomes "the one". In some real sense she doesn't see you as an person with their own life who is in a relationship; her view of you is largely colored by what you mean to her and her dreams. It's by no means a 50:50 partnership, two adults enriching each other's life thru friendship, caring, thoughtful gestures, supportive and wanting the best for the other person. And due to her insecurity and immaturity she is terrified by the thought the real world might not match her fantasy and is in need of constant reassurance. Hence the insatiable need for contact (both physical and on the phone). Hence the insecurity that has her search your phone list (and who knows what else) for evidence that there might be some other girl out there, that you're not 110% devoted to her and that your every waking thought isn't consumed by her. Hence her questioning if you're "being good".
The good news: this is just a phase many girls go thru. From your description of her (sweet, smart, funny, etc) she's going to make a wonderful girlfriend and lover. The bad news: not for you. Unless you're incredibly lucky, she's just not going to get over this phase while she's going out with you. It seems to take a broken heart (or a few) until a girl figures out that she can't demand constant reassurance and constant attention if she hopes to keep a boyfriend. And the future relationships won't come with the emotional baggage of this being the first one she's slept with.