Jennifer - I am replying in hopes that my comments will increase the likelihood of getting an answer to your question from a Team Member.  Perhaps PC was used since the sentence also includes 'au XVIIe siècle'?  Not sure if a French person would consider that phrase enough to trigger the use of PC. 

Hi Jennifer...may I give this a try...also with the hope of triggering further comment. I think the 'j'ai vecu' part is very easy . An action of the past done and over with. However long, it was still one life, with a finite start and end... a discreet action of the past... which is one of the hallmark criteria for using passe compose over imparfait.

'Je faisais partie' is imperfect because she was  part of the French nobility and that never really ended. She is a dead noble but even today would be considered to be part of the french nobility of that time.  One can also look at it from the perspective that 'faire partie de' is an 'expression of a state of being' here (one can substitute 'elle était une noble' ) and the imperfect is used for state of being in the past.... basically she was what she was and never stopped being it but she stopped living. 

"J'organisais". Here the imperfect is used because she is describing 'habitual actions of the past'! She used to organized literary salons.

Notice that "J'ai été la première romancière" is in the PC... because the 'instant' of becoming the first .... was a discreet time event. She  remains recognized  in French history as achieving the honour of 'the first' but THE achievement was a one time  discreet action of the past . 

I use the term 'discreet' a lot but it was explained to me as a brilliant test for the 'PC over the Imperfect'... was it a discreet action(s) of the past... understanding that 'discreet implies a finite start and end'.