1. No; if she has a current Canadian visa as of the date of the trip, she qualifies for an exception even if she's not going to Canada.
2. Probably not. But she can show an itinerary printout to do the terminal transfer.
3. Yes, thousands of passengers have done it 'recently'.
4. It is never ideal to miss a flight. I hope the connection is not too tight. But LA will do what they can if the flight is missed. Of course each airline has its own PNR, this is standard. But it's a single ticket and that's what counts.