Dear Riot: How do levels work?

Experience and gold gain are something completely different. Even if you miss a creep, you still get full exp. Maybe Jinx was just longer on lane, thus draining more exp from minions? Or she took few jungle camps? Or her support was sometimes away from her so she drained full exp from minions? Also, kills don't give too much exp.

She has more experience....

Jinx was most likely CS'ing alone and taking some jungle creeps where she gets more experience per CS and doesn't split it.

Experience is gained from being around minion deaths. Champion kills grant a bit of experience, but even if missing more cs, Jinx will get more experience if she stays in lane longer.

If the support was out of lane for any reason Jinx would have been getting solo XP, which is about 30% more XP than you would be getting if your support was there, the 2v1 situation would also contribute to the lower creep score as she would be getting zoned.

Let me guess, both of your kills are on her support.

This means that she has spent a fairly long time in lane solo (Meaning gaining solo xp) which, while almost without a doubt costing her a lot of farm to be in a 1v2, has granted her a lot of time generate an XP lead. Especially if you got both of those kills very early on, because a kill is only worth 50% of a current level's XP if killing a same leveled champ. And odds are you killed the support level 1 or 2, and killed them again before they could level up to 3 or 4 again. This means they would be only worth aprox a total of 50% of a level up by level 5 or so, and Jinx had gotten what, 2+ minutes of solo xp? That would be 4 waves of solo xp to get ahead with.

maybe she had a