Here is my opinion based off of my experience as a retail manager, my knowledge of
Walmart's policies, and what I have read on this incident. Note, this is only my opinion and is not statement of fact.
Coupon lady was at Walmart and attempted to use a coupon from a competitor. From what I can find, Walmart recently changed their policy to no long allow this though they will still price match ads. Coupon lady didn't like that so she got upset and asked for a manager. The manager comes up, explains the new policy, and that is that...
Except coupon lady gets mad because she still thinks she is right and the manager is wrong. So she pulls out her phone and starts to record. At this point, the manager most likely says to stop recording and it is against company policy for her to be doing so. The manager will not bend the rules for the coupon lady and coupon lady gets madder and madder.
Now, we have not heard Walmart's side of this, however, I would not be surprised if coupon lady didn't shove her phone at the manager. The manager then reacted by swatting/slapping at it. This would be a normal reaction if someone tried to force something into your face. It would explain the reaction and why (as of yet) nothing more was said about that part of the incident. IF this was what happened, then the manager could claim she was worried for her safety at that moment.
This would explain the phone call to police and the insistence by Walmart security that the coupon lady needed to return to the store. I also would not be shocked if this was not the first issue the store had had with this person. A company will not just ban someone for nothing... it usually takes a very serious incident where the safety of employees was in question and/or a history of behavior.
I know that is some conjecture, but I have had a similar incident happen to me. The customer was so irrational about a situation that I seriously worried for the safety of myself, my associates, and my customers. Luckily she left and my store manager decided not to pursue it further, but she was also banned from our store.