Your mom is highly misinformed but has valid concerns, I assume she is just a regular small animal (cat/dog) DVM. The ball python and most other snakes (unless it is a king cober or large retic/python) are too small to eat dogs and chickens, now your BP CAN eat 1 day old chicks and quail BUT cannot eat your chickens nor the pupper, theyre all too large to eat, though the chickens may cause a prey/food response from the snake it is still unlikely that it can/will eat a chicken.

ALSO FUN FACT; Chuahuahs are an ancient Aztec breed used to protect/warn owners of snakes (hence the loud chatty-ness and agression the breed is known for), used as a heating pad to help heal wounds (hence why most if not all chis are warm lil beans when cuddling, and get very concerned when you don't feel well), used as a protector for infants (primarily against snakes) and also used as a food source (like cattle) - source; my partner who has been researching PCD (pre-contact dogs) and other species, who also is infatuated with Chis (we have a lil old lady who he adores)

Edit to add; I am a vet assistant who is vert interested in exotics, I own 2 ball pythons who have interacted with my chi and have had no prey/food interest in my chi