Lump on inside of drumstick!!

[MissChicken]

My BB Red OEGB hen has a painful lump on the inside of her drumstick. She can't stand very well and when she does is hunched over and her feathers are very ruffled. She just sits there and has never been very friendly but she let me pick her up and examine her without struggling. She is pale too.

Please help she's not looking good...

 

[MissChicken]

Update- She can't walk and her droppings are pasty & smelly. Her vent looks red and irritated