Is she broody or is it something else?

[Crossy]

My one year old hen Scarlet has suddenly gone very quiet, stopped laying and started to be a bit reclusive. She looks utterly depressed on a morning and all she wants to do is sit in the nest box. I thought she could be broody and so have been shutting her out on a morning and by the afternoon she has perked up, is running around more with the others and is more herself. She isn't that interested in food on a morning and is only doing rather runny watery poo's. This afternoon she has eaten more but her gate looks a little wide when she is moving around. She doesn't want to socialise on a morning and looks very fluffed but also a little under the weather. I have checked for any signs of illness and she isn't swollen, doesn't have a runny nose or eyes, her vent is the right colour and so is her skin but she was very hot this morning. She doesn't seem to be truly broody from what I have read so some advice would be good if anyone is able to help. She has been like this for about 5 days now but it could have been going on longer as I have been away for a week on holiday and someone was looking after the girls for me.

Thanks and I hope someone can help.