How can I change things around with this relationship, there is a lot at stake?

I met a girl 6 months ago, shes in her late 30's, I'm in my early 30's. We were together since the day we met. Of course we were madly in love at first. SHe has a teenager, I have a toddler from previous relationships. I've since moved in to her house we've talked about marriage and kids, gone on a tropical vacation, found out shes pregnant. She has stress at work , financially, and some minor bothersome(non life threatening) health issues. The stress has really taken control, I've tried to help her financially, emotionally as much as I can . I'v e given 110%. She said she has been feeling depressed, but ures me its not me. life changed a bit, but is still ok. I want to make this work out , I bought a ring and want to propose. It seems she takes stress out on me because I'm the closest one to her. She is very independant and strong minded. It seems that we bicker almost every day. I just want it to be the way it was or something close to it. I see a very strong potential in us.