It will get better - the first couples weeks will be the hardest. I understand about the C-section thing - btdt - twice. Very hard.
She will have to adjust - I have made a point though of meeting the babies needs first if at all possible. 2 year olds can understand that they need to wait (even though they won't LIKE it

) A newborn doesn't and can't understand that. I do talk to my older ones about what they were like as babies - how they used to cry and need to nurse a lot and need to be changed and all that and that *does* sink in after the first adjustment period passes.
So while - yes - sometimes a baby has had to fuss while I change on older kids diaper or take care of an owie - I wouldn't let a baby fuss to just play with an older child or get them something or for anything non-urgent. I think it's important to model the taking care of the baby for the older children. My kids can't stand hearing babies cry - if a baby starts crying in a different room then I am in - they come running calling for me to get the baby. I wouldn't EVER want to model for a 2 year old that it is o.k. to let a baby cry.
oh and the hitting - ugh - dealing with that here also. Maddy hit Megan, Melissa, MIchael (who hit her back), Maribeth AND a visiting friend's dd today. I don't have any great advice other than supervision, disussion about not hitting and consequences (loss of a toy if she used a toy to hit, time out, going to her room to cool off) - but she's still hitting.
With the baby though - don't ever let the baby be with the toddler out of your sight. Hard to do - I know. Michael hurt the babies when they were tiny a lot just being rough (but not maliciously) and Maddy hurt them because she wasn't happy having them there. So lots of supervision in the beginning - I remember taking babies to the bathroom with me (I kept bouncy seats in there) so that they wouldn't be left unattended with toddlers.
oh and I wouldn't fight a food battle with her right now at all. My kids ate less than healthy the first month or two the babies were home.Lots of french frys and chicken nuggets and juice. Maddy even went back to milk in bottles. Not ideal - but their lives just got turned upside-down - food was one area of trying to get some control back. Just give her some space to adjust. Melissa - my oldest - was 2 when my 3rd was born and now at 5 years - doesn't even REMEMBER life without Maddy (or Michael either - she was 14 months when he was born).
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~ Cheryl ~ single mama to
Melissa (9), Michael (8), Madeleine (7)
twins Megan & Maribeth (4)