Thanks Carol, much appreciated.

Eileen, I'd say uncle Ted looks about 3, give or take some months; on that basis the lady could be either aunt, but it would mean Elizabeth died not long after the picture with Ted was taken--the feasibility of it being her might depend on what she died of.
Looking at the images below, if it's Sarah she would have been about 41, Elizabeth would have been about 36. To be honest I don't think either aunt fully fits the lady in the photo with Ted. If I were to choose one, I'd make it Sarah: despite the different styles, her hair is parted in about the same place in both pics and her nose/mouth/chin relationships are closer than that of Elizabeth who has a fuller face, larger chin and closer-together nose and mouth. There are some similarities to Elizabeth as well but, on balance, if there are no other possibilities for a "favourite aunt" I'd have to go with Sarah.
Peter