Has it gotten any larger?
I would keep an eye on it and have a vets # on hand.
Also there is a form or questionnaire here to fill out when asking health related questions.
Best of luck.
Bumps like that are usually a calcium build up from an injury. Calcium rushes to the area to repair the injury, forming a bump. Seeing as it's along the ribs, probably had a little fall at some point in time.
Is this a male or female? Looks female to me. Males have a spur on their back heels. Just make sure you are supplementing properly. Calcium w/o D3 every meal. Calcium with D3 twice a month, and multi-vitamins twice a month(some vitamins have D3 in them). If that is a female, she is looking to be the age where she will start laying eggs, need to provide a lay bin. Eggs could be another reason why she has the bump. The body will draw calcium to form the egg shells - extra supplementing is needed during this time.
She looks pretty healthy in that one picture you provided, just double check those things I mentioned and all should be well