The 10-year-old and her 8-year-old brother, Skylar, opened for business a few days ago and say they plan to staff the roadside stand for about four hours a day.
A spinal cord injury left the cat partially paralyzed. The children's father said a veterinarian has recommended amputation of the leg so that Patches can have a more normal life.
The cost of the surgery, medications and other care could run as much as $700.
For thirsty passers-by, the cost of helping out is just $1 for a bottle of water and 25 cents for a packet of powdered lemonade or fruit juice.
Aspen said she'll "do this as long as it takes" because Patches is one of her favorite pets.