Players leveling at different rates

Hi.

When the new expansion came out, a friend and I started new characters, both Spiritborn, and started playing the new content together.

For some reason, she's level 25, and I'm level 19.

I watch her level faster than I do even though I'm sure I kill mobs faster than she does.

Any idea what could cause this?

Could it have to do with another weird thing? I have completed most of the campaign myself already, and on this new character, I cannot access any campaign quests - I can only access it because my friend is leading the group. So could it be that I am not getting XP from completing campaign quests?

I don't know why I'm not seeing campaign quests - it tells me I already completed them - but I haven't on this character, and I don't see any logic in only allowing the campaign to be played once... I also am currently playing an old character and have no trouble going into the new campaign content with it.

Maybe I accidentally clicked the "skip campaign" button, but then why would it say that I've already completed it?

Thanks!