Hi,
If new varibale is not appearing in 'Quey elements-> Variables', try 'Quey elements-> Query'.. Select the query where you have used/created the new variable.
Select Grouping = Only necessary Objects and Display = List.
Now right click on every component and select 'Do not transport any below' except for your desired Variable in query elements.
Hope it helps.
Regards,
Prathamesh.