Any idea what wrong with my hen?

Just been out to the run and one of my hens isnt looking too good. Her tail is down and on closer inspection she has quite a large egg sized lump on her neck/chest. I've had a feel and she didnt seem to be in any discomfort whilst i was feeling, its quite hard not soft like i expected it to be. I just offered he some apple and she didnt take it, any ideas? Any advice/help would be greatly appreciated

Sounds right. Hope shes OK.

Daisy seems to be a bit better today, she was bright and perky this morning has eaten and has had a drink. she now hiding under the coop out of the rain, i'll keep an eye on her.. thanks for the support and advice