Crabby, that's a terribly irresponsible thing for your mother to do if she is fostering animals! Poor kitten!
Check the kitten's gums. Assuming this is not a black kitten, the gums should be pink and leave a white indentation if pressed with a finger. If they are very pale white, she is in shock. Also check her eyes. If they are dilated even under bright light, she could have a concussion. Make sure she drinks enough water. Touch the kitten's sides. Does she wince in pain? If so, the dog might have bruised or fractured ribs. If a fractured rib dislodges it could go into the lungs.
If she'll let you, wrap her up in a blanket to keep her warm, as she will get cold from shock. Maybe call your vet and ask if there is anything else you can do or any other signs of shock you should be aware of. It would be better to spend $40-60 for a checkup than to wait until any injuries she could have gotten become so serious that th vet bill becomes humongous. The foster group would not be happy with your mother.