What Causes Bump On The Right Side Of The Neck After An Accident?

my daughters had an accident about 2 months ago they were in some go carts at a skating place when one of them crashed into the others go cart, one of the girl s was complaining about her back for a while like 4 weeks she couldn t go in and out of the car without pain she could not even bend, but after a few weeks everything went back to normal she could play and stretch without pain, then about a week ago she was playing and dancing and moving her head to the sides when she felt her neck was hurting really bad and could not rotate it without pain. now she has a bump on the right side of the neck and on the back, can you tell me what this could be, and if you think is related to the accident she had, should I take her in for an MRI?