They most likely have everything booked about 3 months ago. . .luckily it is the off season so they might be able to slot you in. If you phone the week before I can guarantee you it will all be booked up. . . you can hope some one has cancelled, but my recomendation is to phone asap. . .if your mom decides she doesn't want to go you can always cancel.
The California Grill is one of the hottest places to eat in WDW. You can phone to make reservations 180 days in advance, and believe me when I say there are sometimes when the restaurant sells out the 180 days in advance! But like I said it is the off season so you have a good chance of cancellations and openings popping up.