Take another look at the sentence:
Brushing her long hair, strands fell into the sink where they got washed
down the drain and clogged the pipes.
Brushing her long hair, a participle phrase, comes right before strands, an illogical target. People, not strands, have hands that can hold a brush! Before you continue, review the rules for misplaced and dangling modifiers.
Go back to the sentence to try again.