Based on the "classic" costume she's wearing in that flashback, it would have to have taken place before the Avengers West Coast were disbanded, since after then, she doesn't go back to it until last year, so it's somewhen around 1990-1993 (possibly after the AWC encountered Doom in Excalibur #37-39?).
On the one hand, this means that the changes and boosts in her powers, along with all of the "why aren't more readers noticing and complaining about how out-of-character this is?" behaviour from 1998 onwards can be written off as part of the descent into madness, on the other hand it means there was a period before that where she just contained the "Life Force" with no effects. Maybe what Morgan did to her was the catalyst in it starting it's effects.
Thanks. I didn't read Children's Crusade so I didn't realize the encounter with Doom etc. had happened so early.