Just in case anyone gives you any grief about creating OCs: You shouldn't have to make excuses for creating OCs when necessary, just because a few people have some weird near-religious objection to them. I'm sorry so many fanfiction readers are so messed up that. You made a sound and defensible literary choice! :)
I agree. Sometimes an OC is necessary to the plot. (For example, Carolyn Chapman in ‘Jedi Potter’. Without her I wouldn’t have been able to do nearly so much damage.) The trick, here is to write the OC believably, without making him/her into the much dreaded Mary-Sue.
Thanks for the kudos.