I believe I have already answered this questions. The other commentators are posting some very useful advice and resources.
From what you write, the symptoms actually sound a bit more like Borderline Personality Disorder than PPD, although they overlap quite a bit. I'm not sure that self-injury and suicide attempts are part of PPD, although they may be.
In either case (nobody but a qualified professional can make that tricky diagnosis), you will find immense amounts of advice and support at the online groups for family members and loved ones of those with BPD.
I have a ton of these groups linked on my website for nonBPDs:
http://home.hvc.rr.com/helenbpd
Please do check them out, I believe they may truly be eye-opening and life-saving for you and your own mental health; they were for me. The WelcomeToOz group at yahoo groups is excellent, as is the book 'Stop Walking on Eggshells' by Randi Kreger/Paul Mason, available at:
http://www.bpdcentral.com
Best of luck, and do remember that it is not about YOU, personality disorders are very ingrained, dysfunctional patterns of behavior/coping/thinking, and it takes years of committed therapy to change these folks. Unfortunately, denial and resistance are also part and parcel of the disorder, so there is little you can do from the outside.
You might want to try reading: 'I'm not Sick, I don't need help!" by Dr. Xavier Amador, it's got excellent advice for family trying to coax a mentally ill loved one into therapy.
Helen
Thanks for the advice. I will definitely check out our website. I am at my wit's end with this whole mess. The family member I referred to is my sister, and up to two years ago we were VERY close. Now that I look back, I see that subtle signs were always there, but not constant like they are now. She is remarried to a friend (now ex-friend) of mine and my husband's. Because we recognized what was happening early on and tried to talk him into extricating himself early in the relationship when these things began surfacing, we (ESPECIALLY MY HUSBAND) are the enemy. (One of the many enemies, I should say). She has been married a year, and I understand that she is running around town with a number of different guys, yet she is projecting this behavior onto my husband, trying to convince me that he is running all over town when I know this to be untrue. My husband and I have a very good, secure and loving relationship, and I believe she is very envious of that and wants to tarnish it because she herself is so miserable. Until this all began about two years ago, my family was VERY close -- always getting together on holidays, birthdays, for cookouts in the summer and such. Now we can no longer do this, because my husband cannot be around her or things get out of hand and she makes a scene, meaning I cannot attend family functions and holiday events, because, OF COURSE, I will not go and leave my husband alone on a holiday. This is hardest on my mother, who prided herself and thrived on the closeness of our family unit. This is very hard on her and is taking its toll. My sister claims to really miss me and love me very much, yet every time she sees me she can't stop talking about how stupid and blind I am for "letting my husband get away with what he is doing." Doesn't give one a real "warm & fuzzy feeling." I hate being around her, and get sick to my stomach if I know I am going to see her somewhere.
Well, enough rambling. THANKS AGAIN FOR THE ADVICE!!!