And what do you do when everything else fails?

Timeout? I remember being locked in a room for 20 some minutes till I calmed down. Being handcuffed & put in the back of a cop car is traumatizing as hell compared to being locked up in an empty room for awhile.

Schools don't call the cops because a kid scuffs their toe on the ground. The cops are the last resort,

Can you prove they were in this case? Or are you just saying they should be?

I am curious what the fuck was going on in this kid's life to make her think that acting this way was okay.

Say the person who has never been around 3-8 YO children for long periods of time.

There's your real villain. Not this cop.

He did handcuff a crying child, against policy. Traumatizing children is not okay. Even if the child was throwing a temper tantrum, there are better was to handle a 6 year old.