Its better to keep piggies together as this will aid there healing process. It will only cause more stress seperating. So if you can keep a close eye on her then i would keep them together.
As with the critical care, best to get the normal stuff, as weibke has said. Fine grind is ok, but has been made so it can fit down feeding tubes in the vets, ive used it a few times for this. Its the same stuff, just finer. Probiotic may help too, but critical care does have this in it too. But no harm in adding more in. Fibreplex can also be a great supplement to give.
x.