Your girlfriend really needs to get her hormones checked. I have severe mood swings, and after years of suffering, I finally recognized it's a definite pattern. If she has ever taken birth control, that may have made her mood swings worse, which is what happened to me. I got the birth control shot, and it totally messed me up. I use to be pretty mellow. I get into those moods where I over analyze every detail, and go into this negative thoughts loop. It's real torture for a good part of the month. Just be sensitive about that, but also encourage her to get some tests.
Another thing, I have a boyfriend with kids, and I realized I cannot say anything about how he wants to spend his money on them. So, I had to learn to just leave it alone. If she wants to spoil her kids, then she has to pay for all of that expensive unnecessary stuff. All you can do is let the kids and her know where you stand with that, and give up trying to change her mind. The problem is that she can't work because she has kids, but wants another one???? For the love of God, don't have a child with her before you resolve this issue. It will not make anything better, only worse! And then guess what? You could break up, and be stuck paying child support. I don't understand why she can't work PT. She needs to get her hormones balanced, and then become a grown woman about her responsibilities as a parent. Her family doesn't HAVE to look after her kids either, it would be nice, but it's not their sole responsibility. Sorry, but some parents these days expect everyone else to look after their children, get mad when others don't want to, and then have another kid! Please be wise.