No you shouldn't need a heat lamp if it's summer there. i get the electrolytes/vitamins packs at a local place called Jeffers, not sure what you'd have down under that would be the equivalent, check with your feed store.
http://www.jefferspet.com/products/vitamin-electrolytes-plus
likely she has internal injuries, could be broken bones, just keep her warm and in a dimly lite area so she can rest and recover. provide electrolytes/vitamins in the water and quality feed.