If the girl didn't 'mean to cause problems' then she WOULDN'T have said anything about it on Facebook - TO YOU. I am sorry, but I have to call BS on that one. She didn't mean for it to cause problems for HER, and now that she has realizes that it can cause problems for her, she is backpedaling very quickly.
You are in the right her, NOT her. Your team leader doesn't get to decide how big of a deal this is for you, only YOU do. Your team leader just probably doesn't want to do the extra work to take it to the HR department. It isn't about what your team leader wants to do, it is about what you want to do. I can't believe the other person hasn't contacted you - even with a note - apologizing for their behavior!!!!
From my perspective you have three choices:
1. Tell the team leader that you are uncomfortable being in a meeting with the other lady, and have no desire to talk it out with her. She has already communicated her feelings clearly, and that you would like to know what your team leader plans to do to make sure that you have a comfortable work environment.
2. Tell the team leader that you are uncomfortable with a meeting, and while you understand her feelings to keep it 'in house', you would like this escalated to the HR department, and handled from there. Period, end of story.
3. Go to the meeing, and see what happens. Don't promise or give away anything, and depending on the outcome either let it go or escalate it to the HR department.
And, as far as this being 'outside of work'...so what. The internet has made our private lives available to our work. How many companies screen candidates facebook pages before hiring them? If you were to get arrested for something in your private life, would it affect your job with the company?? I bet it would!!
That said, you can't blame the work girl for what your family has done. Those are separate issues. She might have brought something up, but it isn't her fault that V felt obliged to pounce when she felt like you were down. Honestly, the way I would handle V would be to call her out IN person, the next time you see her in a family setting. She sounds VERY passive aggressive - to make snide comments about someone, knowing that they can see, but not *really* able to pen the message on her.
I wouldn't be RUDE to her but I would say something (when there was an audience) "You know the message you posted about me on Facebook was really upsetting to me. I understand that getting pregnant was not the ideal thing to have happened to me, but it is a consequence of a choice that I made, and I am an adult enough person to take responsibility for my actions. Whether or not you think I am going to be a good parent is not only pointless, but also harmful for this baby, as so much anger and negativity causes me a lot of stress, and that is never healthy for pregnancy. In a perfect world, maybe things would be different, but this isn't a perfect world, and I am doing the best I can. It is really sad for me that instead of having family members who can emotionally support me right now, when I need it the most, they instead write nasty things about me for the world to see and make me feel really bad."
And, leave it at that. I really think in situations like this, killing them with honesty and confronting them with it is best. Most people hide behind Facebook, and would NEVER say to someone what they say on there.