Even though he is busy and you feel he is not around much, for your DD seeing him there every day is enough. (If that makes sense). She would be very aware of him going then coming, having meals and just being a presence in the house.

Do you have a picture of your DH that you can put onthe fridge for her. We used to do this for the girls when their dad had to be away and they would say goodnight to him and sometimes just having it there to look at was enough to settle them when he was missed. We used to change it every year and it became a joke if it was missing or not up to date, it is still there even though they are now adults.

Can you talk to him on skype while he is away?