EC.Mason, this info is NOT meant as an insult to your daughter's hopes, or you. It's merely educational info.
To many people,
any "old-looking" iron ball has just
got to be a (valuable) civil war cannonball -- or Grapeshot ball, or Canister ball. But in actual fact, millions more civilian Industrial-usage iron/steel balls exist than Artillery balls.
So, as NOLA_Ken said, super-precise measurement of the iron ball's diameter
and weight are needed for proving whether or not it is a civil war (or earlier) Artillery ball. When you've made the super-precise measurements, look for an extremely close match in the US (and CSA) Ordnance Manual's artillery-ball size & weight charts, viewable online for free at:
www.civilwarartillery.com/shottables.htm
Also, because some civilian Industrial-usage balls may coincidentally be the same size as an Artillery ball, it's important to check the history of the location where an iron ball was dug, to see if any Artillery was ever used there.
For your daughter's sake, I sincerely hope her find matches up with a ball in the Artillery ordnance Manual's charts -- and that artillery was used at the location where she found the ball.
If it turns out not to be an Artillery ball, please use the occasion to educate her that we relic hunters must "fact-check" our metal-detecting finds. (And, we relic collectors must also fact-check a relic before we pay our hard-earned money for it.)
Please pardon the delay in replying. As Breezie indicated, I just got back home yesterday evening from a 4-day trip to the annual civil war relics show in Mansfield Ohio. Had a great time seeing many old friends and hundreds of tables full of civil war relics.