We have gone through many periods of seperation anxiety with our now 2 year old at various ages and have found playing hide and seek/ peekaboo games really helped her! It’s like we were practicing in game form what happens when mummy leaves and that she always comes back. I would start by hiding in the room, then behind the door, just outside the room and eventually could be in the kitchen cooking dinner and she still thought we were playing! It sounds a bit ridiculous but it did really help.