Help my Favarolle is acting sluggish!

[jbowe]

My daughters Salmon Faverolle has been acting lethargic and "yawning" a great deal. I have also noticed that she is spitting up a little as well. She is eating and drinking however. This morning I picked her up and noticed a large "blister like mass" on her chest that is about the size of her breast. When I massage it gently she spits up a little. I separated her a day ago and started her on antibiotics. Has anyone ever encountered this?? What will help her, She is only about 10 weeks old and I don't want to lose her.
Thanks!