The lawsuit also names the Madera Unified School District as a defendant. Among other things, it alleges that the school failed to notify Graciela’s parents that she did not show up for class that day, as required by district policy.
This makes a bit more sense than suing BMW, since if the school somehow contacted the family earlier perhaps (depending on when they'd call) they would've thought to check the car. That does not absolve the family from responsibility of the stupid act of locking someone inside the car.
Unless there was a specific DoT rule that required cars at the time to have an "escape" feature if a car was locked from the outside then BMW is not really at fault.
The excuse they didn't have the manual because it was a 16 year old car is BS. Manuals for old cars can be found easily. A quick google search returned this:
http://www.mikerophonerecords.com/bimmer/e36manual.pdfand in page 31 it states:
Never use the keys or the remote control to lock an occupied vehicle, as it would then be impossible to unlock it from inside.Still the whole case seems more like an outburst of grief and guilt than substance. I think they're trying to make BMW settle out of court to avoid bad publicity.