Oh c'mon. A lot of people say that drugs are bad and it's a proven fact, yet there are still many people who use em. Stupidity is everyone's epidemic. Besides, she wasn't trying to "kill" the sorceress... She was trying to seal her powers. Rinoa just didn't know how powerful a sorceress can be although she's one. She isn't a SeeD for all we know. Squall is a SeeD, but he was no match for the sorceress too.
Oh one more thing, she couldn't really fight because Edea 'stunned' her... or maybe weakened her to an extent. Hmmm...I just realized that if that bangle reacted on her, that only proves Rinoa's a sorceress from the beginning...