Screams at nursery

[Roxiet2013]

My dd is 18 months old and has been at nursery since she was 1.
Obviously at the start she'd scream when I left but then she didn't mind anymore and all was fine.
However for the past month or 2 she has screamed everyday when I go to leave. She walks in happily but as soon as she realises that she's in her room and I'm going to leave her she clings to my leg and screams the place down, face planting the floor and everything.
I stay calm, give her a kiss and tell her mummy is going to work and will see her later but it's the same every day.
She's fine when I pick her up and happily playing then happy to see me. They say she's fine once I'm gone which I don't doubt at all, but why is it like this again? I thought we'd got over the screaming stage. It makes me sad and hate it.
Is there anything I can do to help it, will she get better again?

I would imagine this is developmental in that, when she first started, she cried because she realised you were leaving and felt distressed but stopped when it became more familiar and the distress reduced.

Now she understands a little more about the world and knows that she can affect your decisions but showing distress, she is doing it for your benefit. Not that she isn't upset by the idea of being left (18MOs aren't that manipulative) just that she is aware that, if she doesn't want something to happen, you can make it change in response to seeing her crying.