P.M.
I think what others have said is correct. Add to that that she knows she can count on you. She takes you for granted, literally, and at her age this is an indication of trust and relaxation.
But littles are very immediate in their interests, and when you show up while she's engaged in something else, it will take her a bit to switch gears. Seems completely normal and healthy to me, and a good sign that she's not unhappily waiting for you throughout her day. Smile, Mommy, she's having a good life!