At the end of the episode, I turned to my son and said, "Couldn't he just bring her to the Fortress and heal her with some Kryptonian tech?" He nodded and said, "Yep."
Now, I know that would take away the emotional impact of the story and all that, so that's why they won't do it (at least not immediately). Still, enjoyed the episode and the fact we get to see Superman so vulnerable.