I am sympathetic to the supermarket staff on this, but I have a feeling this will not turn out well for the store and employees involved. The mother of the 14 year old, Jackie VanDucker, is interesting...let's just say the apple does not fall far from the tree. Is it me, or does mom look like she has a lot of hard mileage on her odometer.
When I was growing up, if you got caught doing this, your parents' wrath would be way worse than merely being detained like this girl was. She managed to escalate a minor juvenile offense to a felony (although I suspect charges might end up being dropped). I do not see excessive force from the store. The only reason this 14 year old is rolling around on the ground with theft prevention is she is trying to flee. The lesson (if the store gets punished for this) is if you grab and go, you are good.
This 14 year old would be better off acknowledging what she did was wrong, rather than trying to blame security. A smart parent would recognize that. To paraphrase Willie Nelson: Mamas, don't let your babies grow up to be Shia LaBeouf