I'm assuming you'll be on the DDP. Is your mom staying in your room? If so, no problem. She just can't exceed the number of A or C credits listed on the card. For example, if you have 3A/2C listed on your room keys, she can get any combimation of CS meals up to 3A/2C meals. There's no requirement that all members of the party be present.
Last year, I frequently purchased meals for my dh and kids who were either sitting the food court or lounging in our room. I never bought all 4 meals at once, because I couldn't physically carry that much, so it was always various combinations of A and C meals, but never more than 2A or 2C at one time.
If you're not on the DDP, no problem. Your mom can purchase whatever she'd like for whomever she'd like. It's only on the DDP when you have to worry about how many A and C you have listed on your room key.