Having been on both sides of the spectrum - losing someone suddenly and watching them slowly fade - I've never been sure which is worse. I'm so sorry for your loss. This is something that is very hard to deal with, I know. You did a wonderful, brave and strong thing by staying by your auntie while she was leaving this world and I'm sure she appreciated having someone who loved her as much as you did by her side in those final moments.
Maybe for the next while, however long you feel you want/need to, get something of hers and carry it with you - be it a watch, ring, necklace, scarf, a photograph, anything - just to hold onto that connection, to, in a way, have her with you while you grieve. I found that helped. It kind of keeps her close even though she's far away. And in time, it will ease some. It will.
You have a good heart and you're strong, just try to find something to hold onto for the first while and come and talk with us here. It's why we're all here.