I love this community. I have had relatively good natural game for a while, but you guys have it down to a science. This is an area where I can give back some advice.
My tried and true principle: go until she says stop.
Sex is the most fantastic thing in the world. Men and Women are hardwired to want sex. Unfortunately, there is and has always been more at stake for women then men when it comes to sex, especially random sex. For this reason you should establish yourself early on in your game as someone whom she is comfortable with.
You seem to have already established comfort, now you just need to turn up the heat. Build up slowly when making out: begin with soft kissing on the mouth, neck, and collar bone. Then use your hands to apply firm palm pressure to her erogenous zones, I go for the lower back and neck. This works well for two reasons, when you have your hands on these parts you can literally feel her heating up, its great, and you are in complete control of the situation. You can press her body into yours, throw her around, whatever.
Now begins the arduous process of getting her warmed up. Escalate the physicality until you feel her begin to pull back (usually this is extremely subtle, be sure to look for it), once she does go back to soft kissing with limited body contact. Escalate again, then retract for a few minutes. Most of the time she will begin to try and escalate, pull back, make her wait. Each time you escalate go a little further. Reach up her shirt, grab her butt, be an animal, then go back. After 15-20 minutes most girls are tearing my cloths off, but sometimes it takes longer.
(Protip: learn how to give head) Once you get to the oral stage, she'll be all yours if you are good. Confidence is key during sex. Here you are in control. This is raw, primal instinct. You are the man and she has to know it.
Keep in mind, this works during sex as well. Ever want to try anal, or that weird shit you saw on the internet? You kinky fucker, haha.

Escalate/retract, repeat. Girls will do just about anything if you ease them into it correctly.
Peace,
Calison