Hi carlosmc. I am new to this forum but not to bipolar disorder. I am not suffering from bpd but 2 of my children and a brother do. My husband has seasonal affect disorder, which is considered a very mild bpd.
Your wife is sounding very unstable right now. She is not taking her meds so that will cause huge shifts in her moods. There are many medications out now. Perhaps her doctor would be willing to try something other than lithium to help her control her bpd. Try to encourage her to go to the doctor. Let her know that you know she is miserable and life shouldn't be this painful for anyone. Childbirth often causes women who have bpd or are predisposed to bpd to have erratic shifts in mood. The hormone levels are shifting and contribute to the mood swings greatly. She should see her doctor based on that alone.
Offer her support, try not to be too judgmental. This is difficult because she probably targets you for all of her aggression and hostility. She does this to you because with you feels safe, secure, loved and knows on some level that even though the behavior is terrible you will still be there and love her. I am the happy recipient of my son's aggression and hostility. He can be pretty angry and abusive at times and most of it comes at me. It is exhausting and difficult to take. Try to remember where this stuff is coming from. She is not well. She feels horrible. Her brain is probably on overload, constantly ON, with thoughts going, going, going. This would cause her to feel agitated and irritable.
Getting her to a doctor is really necessary. She sounds like she is cycling. If she does not get the proper meds to help her she will likely get worse. Tell her that her children and you need her, love her and want to be happy and healthy.
I hope this helped. All the best.