Sydney Frankle was the sister of Gary Frankle.
Sydney's brother Gary wanted to become a witch. Sydney was aware of his interests, so when he arrived at the breakfast table one morning acting strange and asking their parents if they'd noticed if he was interested in the occult and if he knew Latin, Sydney was equally stunned and amused by his behavior. She was even more amazed when he asked them if they knew of any old leather bound books with funny writing on them that he might possess.
When out of earshot of their parents, Sydney confronted her brother, who was actually Sam Winchester, still reeling after Gary had successfully cast a spell to swap bodies with him. She accused him of having "sprung a leak," pointing out that if their parents ever found "that creepy old book" of his, he'd be grounded for a decade. She of course didn't understand why he would bring it up at the breakfast table. She gives Sam enough information to find the book in Gary's locker at school.