First, I don't understand how either 1) merely stating a type in a thread with a discussion (presumably) taking place without any supporting evidence or 2) posting in several pages of threads without, again, any evidence can be perceived by a poster as contributory.
Second, I think Lavigne is a standoffish entj. YouTube - Charlotte Church extended interview with Avril Lavigne 1of2
So clearly here, she's being interviewed by another, and the interaction patterns are interesting to say the least. Has she changed since her younger years? Not really, apart from age (inferior/tertiary-Fi). One moment they'll be chatting about rudeness/swear words using a 50-foot pole (inferior-Fi); the next her interviewer explodes into temporary hysteria (dom-Te), and while she doesn't necessarily replicate that behavior, her body posture remains straight, legs are crossed (suggesting comfort). So she's essentially at ease throughout, despite signs in her speech that might say otherwise.
So initially I was thinking reserved entj, now strongly considering istp. Interviewer must be a dom-Te user. Avril does seem mostly at ease, though slightly put of by either that energy or revealing more than she would rather towards the end.