is aela essential
There are different notes across various pages regarding the essential status of Aela, Vilkas, and Farkas. As of now, this page says it's after completion of the Companions questline that she is no longer essential. I'm not sure which is actually true, though. saw at this page: http://elderscrolls.wikia.com/wiki/Aela_the_Huntress that Aela is still essential, even after you have married her, if you haven't end the quest of Totems of Hircine.