I am quite similar to you in some ways op in that I'm stubborn and determined. I've had two emcs and was discharged 12hrs after the first one and 32hrs after the second one.
When my ds (my youngest) was born, I probably experienced a lot of what you're feeling now. I was torn about leaving dd (emcs was a definite possibility, if not the likely outcome) and as a fairly attachment orientated kind of parent, I hadn't been away from dd at all. When I found out I was pregnant, I did start slowly introducing dd to the idea of being put to bed by grandma, grandad and/or daddy so that when her brother was born, there wasn't too much new stuff going on. By the time I'd been in labour for 3 days and knew that an emcs was the only option left, I had no worries about leaving dd though I knew I was going to desperately miss her. I had put in the groundwork first though. It was my job to leave my firstborn as prepared as possible for what was coming.
I asked for dd to be brought to me as soon as I was back on the ward. She met her brother when he was about 70 minutes old. I had the feeling back in my legs by then and was able to have dd up on the bed for a cuddle and a story, we chatted and we talked about her new brother. She stayed for an hour or so and then dh took her home. I was up and about an hour later, caring for ds alone. I'm very fortunate that I don't have any pain following cs and am up and mobile v quickly, discharged promptly and able to get on with things. I stress, this is luck.
DH could only afford a week's leave and he lost 3 days to my labour. So when ds was 4 days old, he went back to work and I had a school run to do which was 2 miles on foot and 2 miles on a bus with a 4yo and a baby in a sling. I was 4 days post op and had no choice but to get on with it. I was determined and capable and no doubt plenty of people were horrified but it was just the way things had to be.
But and it is a big BUT, it is not remotely possible to give your eldest 100% of your attention at all times. She will have to wait sometimes. It might only take a poonami of a nappy where your ds has got it up to his neck and down to his toes and is trying to stick his hand in it and eat it and at the same time your dd is sobbing because she can't reach something/do something/has pooed/is wet/has banged her leg. And you will have to prioritise the baby. Or when ds was about 19 weeks old he had a cold and he got slowly worse and worse and then suddenly got much worse at the point that I was supposed to be collecting dd. I had to send anybody available to collect dd as I took ds to A&E where he was admitted into a high dependency unit with double pneumonia. I had no choice but to go with my poorly ds and dd had to deal with me not being there. It's life and it happens and as a parent you prioritise the most vulnerable member of the family. If that is the baby, then your dd will have to wait.
You know what though, it's fine. It's a good lesson. For both dc. That sometimes their needs are paramount and sometimes they have to be patient. Just don't set yourself unrealistic goals of never having to leave your eldest waiting. You're having another baby now and that boy also deserves a parent who can respond to his developing needs instead of conforming to rigid boundaries which aren't realistic. You'll make yourself feel guilty and like you're failing. Just go into it with an open and positive mind. Not chasing the impossible.