Puffy, swollen face

Hi!

One of my marans has a swollen and puffy face just on the one side and it's been like this for about 4 days.

Does anyone know what may be causing this? We have nettles growing within the pen but they tend to avoid that area and I have seen them catching flies and bees but would have thought that if she'd been stung the swelling would have gone by now?

Thanks in advance!

UPDATE!

Well after a few days and still no improvement I contacted my local vet and picked his brains. He thought it'd probably go down in a couple of days but said to get in touch if the swelling grew or if any new growths developed. I'm thankful to say the swelling reduced and she continued to lay throughout!