Probably because of that memory issue: that is, Nelis needs someone to make the impressions for the soul to search. Plus, we don't know if any of the Energy Golems were destroyed, so there might be nothing for her to find.
Also, that is another point that hasn't been raised: can she revive hostile beings? Or would their soul impression be such that it will refuse to yield to revival? After all, in TRPG2 she only revived allies, and possibly neutral units, but not enemies. And even then, she couldn't revive all allies (cf Gen. Darkeye).