If (Mama) is the European red breasted robin, they are fairly active around dusk and often one of the last birds to quit singing in the evening and will often continue long after dark under a street light, this is pretty typical behaviour for them. I was glad to mama came back, I think this must be a good sign. You may not always see a beak full of goodies on her return, it could be that she has semi digested grubs etc and may regurgitate them in a palitable form for her young, she may also fly out to get rid of droppings to keep the nest spick and span. Mothers usually know what they'r doing and have a strong instinctive-maternal bond (Hope I'm righit here). I think you are privilaged to be able to view her commings and goings at close quarters without causing any disturbance. Best Wishes.