The name says it all. How does the quest level limits work? My girlfriend just joined my game and I am in ActII and she is level 1 and was able to join. How can she join an Act she has never beat and can she out level the minimum requirements for ActI and never finish the game?
You can join any quest in your current Difficulty if you're invited or joining through the friends list, though there are requirements for stepping up in difficulty - you must have killed the previous difficulty's last boss, and meet a level requirement for the difficulty:
Public games have a stricter level requirement, and require you to have reached that quest.