I have to assume that your sister doesn’t have children and therefore doesn’t understand that what she’s asking is not just unreasonable, but actually not even really possible.
If you’re breastfeeding, you’re advised not to pump before 6 weeks and so what are you supposed to do when the baby’s hungry? Go driving for 40 minutes, feed, then drive 40 minutes back to venue, only to have to turn around and drive straight back because your baby will be hungry again by then?
If you end up having a C-section, you might not even be able to drive yet by that point, so that’d be your DH also joining that farce to ferry you back and forth.
Even if you’re bottle feeding, emotionally you’re highly unlikely to be able to handle that physical distance from your baby. Intrusive thoughts are real and while there might not be a baby stealing your sister’s thunder, the MOH who keeps crying because she’s just had an uncontrollable vision of the hotel the baby’s staying in exploding might draw some attention (the first time I went out without my baby for a 20 minute walk around the block, I was absolutely convinced that my house was going to burn down while I was out and that my husband would forget to rescue the baby - I was in tears by the time I got home even though I could see the house was fine).
I think you might need to show your sister this thread so she can start to understand what she’s really asking of you.