Just stay the course. Leave it outside and let's see if you get new growth in spring. You have several issues. One, it's weak from an extended stay indoors. Two, the new growth it was pushing inside is not hardened off so it wasn't ready for cold. Three, it's planted in muck, so you probably have root problems stemming from watering issues.
Best case, after the end of season fuglies it will push weak growth in spring. If that happens it will be on the road to recovery. Worst case it will die. Happens to all of us. Research repotting, take a workshop or class, buy a new elm in spring and repot it right away with your newfound knowledge. Then we'll be able to get to work.
Scott