6yo daughter with left arm pain

[Conradolara]

Last night my 6 year old daughter complained with her left arm hurting.  She was just sitting in the car at the time and had not previously hurt her arm that anyone is aware of.  She has kept it drawn up as if it were in a sling.  She says that it hurts if she staightens her arm and fist out.  It seems to hurt most in the elbow area.  She doesn't cry with this pain it just seems to be a constant dull pain.  We have watched her and even when we aren't "looking" she does the same thing and she is not a child that starves for attention.  She is a super healthy child with no problems. I was just wondering if this is anything that anyone has ever heard of?