There's no doubt that Élisabeth was a remarkable woman. (The term is used too often, I think, but it really applies to her.) Her ability to survive in the conditions she describes, in the weeks and months following Thermidor, is certainly a powerful testament to that.

It's indeed difficult to say how much help Éléonore would have been in taking care of the baby, since she was only ten years old when the last of her siblings was born--old enough to have helped at the time, but probably not old enough to remember in much detail more than fifteen years later.
On the other hand, I'm not sure when their other sister's (Sophie Auzat's) children were born, but it's possible that if they were born before Thermidor and if Éléonore or Élisabeth had gone to visit her, they could have learned something there about caring for babies. Or similarly, if they had cousins or friends with small children at time... But this is all conjecture of course, and even assuming that Éléonore knew what to do, it would in no way detract from Élisabeth's courage and strength.