First, you need to find out what’s making your toddler so scared. Sometimes children see something on television or out in the world, and their imaginations — which are in full bloom at this age — run with it. But try to get her to talk about it.
Once you’ve determined the source, the same concept that applies to adults with phobias applies with scared toddlers: Exposure is usually the best way to conquer fears. In other words, teach her about it. If it’s snakes that are scaring her, talk about snakes, read books about snakes, maybe eventually even show her a real snake in a controlled environment. That knowledge and experience will make her feel as if she has more control over what’s happening in her mind — and the fears should eventually subside.