Botulism results from a protein called botulin, produced by a particular strain of bacteria. Once inside the body it blocks the nerve cells that cause muscles to contract, resulting in paralysis. At worst, botulin can cause total paralysis leading to death.
Since botulism bacteria cannot survive in oxygen, they form spores that lie dormant until they're in an oxygen-free environment. For example, the oxygen-free insides of canned goods are prime breeding grounds for botulism. Unless such cans are heated properly to destroy the spores, they will awaken and contaminate the food inside. That's why many cases of botulism occur after the victim has eaten canned food.
Honey normally doesn't come in cans, so what does this have to do with babies? When bees collect nectar from flowers, they incidentally pick up botulism spores that get mixed into their honey. Since adults and babies more than a year old have fully developed immune systems and intestinal bacteria that destroy the spores, eating honey is no problem. Lacking these safeguards, a baby that eats honey provides a perfect environment for the spores to activate and unleash their toxin. So keep your baby away from honey. Chances are she's already sweet enough just as she is.