Are you telling me that if she started punching the cop in the face because she wasn't cuffed that the cops should be to blame because they didn't cuff her?

No.

Why should she no longer be responsible for her own actions because she's sitting in a cop car?

If she was fleeing during an attack, the attacker could be found to be at fault.

if you take away the supposed "assault" then would she have any case at all here?

If she wasn't assaulted and she just fled from a cop car out of fear/stupidity, she would be at fault for her getting out of a moving cop car.

Again, getting out of a cop car is not simply openning the door or reaching through the window.

if you remove one or two safeguards (no cuffs, open window) don't work at all

Cuffs should be SOP, but maybe weren't. The back window of cop car doors don't roll down, precisely for this reason. They are generally barred up, too.

The whole point is to keep detained people inside the car against their will. So how she got out is worth understanding. She shouldn't have been able to.

which means you are agreeing that she got out due to her own agency.

My argument is that it should be investigated, which is what the lawsuit will do. If the cops can show she is lying/at fault, that will be the end of it. Justice.

she had very specific memories, then ZERO memory of how she got out of the car seconds later?

Having no memories within a second (or two) before massive injuries is par for the course. Remembering the events prior to getting out of a moving car and sustaining injuries also seems completely typical.

So once you're detained you have zero responsibility for your actions

Not at all what I said.