If your mom's flying into Burbank, can't she take the train to L.A. Union Station?
She would then be qualified to take the bus to Bakersfield. It's slightly out of the way, but it's a way to be "legal" regarding booking the bus with the train, and you wouldn't have to "throw" a ticket away (although you can keep unused tickets for up to a year).
Anyway, to answer your question -- I can't find a layout of Union Station but I recall a bit from my short time there. Union Station is set up with the train platforms in the rear set apart from the station and connected via tunnel. If you're arriving via train, you walk down the platform, descend a ramp into the tunnel and walk into the station.
The station is pretty big. From the tunnel, you'll walk through a crossroads of sorts (splitting off to different tracks and the main part of the building). The giant waiting room lays beyond. This area is well lit and filled with comfortable-looking seats. Off to the each side of this room, there are garden areas. The garden areas to the north is where the Thruway motorcoaches are located.
On the other side of the waiting room, there is more as you head west toward the street entrance. There are lobby areas and stuff, but I didn't see them during my trip through the area.
Edit - The MTA has a
pretty decent map of the station (PDF). The interior of the building isn't spelled out, but it shows where the buses are and many other landmarks.