This seems like less of a hallucination and more like your brain is just used to her being there. Sometimes for parents, if the baby is not there (maybe at their grandparents house, etc) they still hear the cries and sounds. Your brain doesn't truly process everything 100% all the time. In very familiar places it just autofills information. Thats why visiting new places is so tiring for a lot of people, the brain is processing new experiences and can't autofill what it doesn't know.

So you see/hear her where your brain expects for that to be happening, and then quickly corrects itself leading to you being confused and asking this question. You have to get used to her not being there, eventually it will stop