of course I can tell by the chatlog that you two were in fact going back and forth, but again, for all we know this could be her very first offence and therefore only got a chat restriction, if punished at all (because riot actually does give some leniency when it comes to the punishment system)
but the reason they leave others' out is because they're trying to tell you others' actions shouldn't affect your own behavior. at the end of the day though, either one of you could have muted the other, and stopped it before anyone was punished tbh.
also troll and greifers most certainly do not get away, just by pissing you off and getting you to flame back, you are now a flamer, and therefore get punished for verbal abuse. it sucks, but there's a reason its a general rule to not feed the trolls.