Rob is right - the best thing to do is to fix the callee service.
If you cannot change the callee, one of these things may work:
Use variable substitution to access %docA/docB/strC% to access the data at design time. (Note, not %docA/docB[0]/strC%)
Copy/paste the callee’s actual output data structure into the caller’s design-time pipeline. When you save this change, webMethods has a habit of ‘disappearing’ the new data structure. To work around this, either paste the data stucture into caller service signature as a junk input, or hardcode some junk data to the variables you want to retain.