No matter the airline, plane type, or route a flight from the LA area to the SF area would at least be 30,000. Southwest flies as high as 38,000 feet on this route, and even United's CRJ's get up to 32,000 feet or so.
If you really want to try a basic level of altitude, I suggest a prop flight. SFO-MRY could work. It would be on a prop and it wouldn't get above 10,000 feet. If all goes well, I'd suggest then going to SoCal and so on.
If the docs are clearing her, then I would hope to think all would go well. I completely understand the anxiety about it though!
I hope you find something that works and I wish you and your companion the best!
