7 week old turkey with large fluid filled sac on chest

[rucnmom]

I just noticed that one of my 7 week old turkeys has a very large grapefruit sized fluid filled sac on her chest. Any ideas of what this could be? Do I separate her from the rest of the flock?

Unfortunately, I'm considered "new" so I can't post a photo yet. She acts ok but this looks pretty strange.