My goodness, you had a rough first pregnancy and birth... are you sure you aren't having a subconscience fear to going through that again? If it is that you feel you will favor one over the other, I can assure you that each child is favorited in one way or the other, just make sure they are evened out. I use to tell my kids "who is my favorite 2 year old?... who is my favorite 3 year old" and each of the ages, that way they know they are all my favorites. I have to say I enjoyed time with each one seperate and I think that is good, to have total attention from mom. Each year before school, I would take each one shopping, just the child and me, for the school supplies. We also went shopping a lot with all the kids together.
Now I will tell you, my first pregnancy I was excited about. I didn't have a hard pregnancy as you but was in a bad marriage which I left when my son was 3 weeks old.
My second pregnancy with my second husband who I married only a year after leaving my first husband (knowing my second husband for 6 months) I was not ready for another baby on the way. My oldest was just a baby himself. I cried, my husband rejoiced. When I held her I was so filled with love for this tiny baby, just as I was with her older brother. When she was two years old I decided that it was time for another. My overies shut down with the birth control pills. For each month for over a year I had to go to the doctor, have a blood test done to see if I was pregnant and then have a shot to kick start my overies. It took a while but I did end up getting pregnant and there is 4 years between my daughter and her little brother. The biggest difference there was that I had more time alone with him since by the time he was born the older two were in pre school and kindergarten, which was nice bonding for us. My kids are all grown and each have their own life and life styles. I see my youngest most since he lives in this town and the other two live farther away. I can say I love all my children and enjoy time spent with each. Their personalities and busy lives dictate how close we are now. My youngest is the father of my only grandchild and she is the light of my life. I too wonder if I could do justice to another grandchild when I have one, then I just think back on how I felt with each of my babies, I will do just fine... just as you will.
Enjoy your pregnacy and make sure you include your daughter in all the excitment, making it her baby too to keep jealous feelings out. Make sure you let her know that you love her very much and the new baby won't take any of that away.