I am sorry for your friend's loss ... however .... how does one make the immediate leap to "Alaska Airlines stole my luggage" when your friend left a note instructing AS to leave the suitcase at the front door if no one was home?

While I suppose it is possible that's what happened, isn't it also possible that someone other than AS personnel took the bag?

As to what she should do ... she should file the police report, and apparently has done so.

Regardless, in the area of unsolicited advice, she might want to re-think the bit about leaving her front door unlocked. In the world we live in, unfortunately no place is safe anymore.