DD categorizes this partner as a "frenemy," which she defines as a former enemy that she has turned into a friend.
I love this definition of a frenemy! Much better than the love/hate frenemies/rivals pervasive in most of the secondary institutions with which I am familiar.
I agree.
I'm not even sure she knew it was already a word with a different meaning. Language is considered to be a favorite play toy in our household, where inside jokes, intentional malaprops, and invented slang are commonplace, so this might be another example of the latter.
In the same conversation, to the surprise of no one, she announced that her and Frenemy were inventing their own language, which so far consists of (unintelligble) and (no idea, really). She's been playing this particular game with every friend she's had since she was at least 5.