Totally agree with Karla. Any suspicious limp should be checked by a Vet. Have you given her mouth and teeth a thorough inspection on the off chance there could be infection?
Yes, check the Shelter sites and see how many Pits are there with Chihuahuas running a close second. What a shame. :-(
Welcome to the forum.....ALL lumps and bumps need to be professionally evaluated...This sounds like a swollen Lymph Node to me and should not be taken litely.... Swollen nodes are usually indicative of an infection (That needs treated), but they can also be indicators of some very serious issues.....
I would not consider the collar being the culprit until the above is ruled out.....Let us know what you find out......Karla
P.S. On a side note: Please try to talk to your friend about continuing to breed these Pits...The country is already full of too many abandoned (For whatever reasons), dogs....As of this moment, there are 20,056 Pit Bull or Pit mixes looking for homes within the United States.....Yes, twenty thousand!!!!!This will be an impossible feat to fill & sadly most will be euthanized each Friday as the rescues & shelters are over full and over run........It is never the dog's fault, but always human's.....However, it's the dogs that have to do the suffering for it! Please, talk to your friend about adding to the problem......Thank you