Identify the dependent clause: whenever she's nervous, she bites her nails.

The dependent variable is that she bites her nails. Being nervous is an independent variable due to that it doesn't depend on anything said. However, in order for her to bite her nails, she has to be nervous as stated.

The independent clause would be “she’s nervous” because the biting nails part depends on the nervous part, whereas the nervous part doesn’t depend on anything.
I hope this helped! :-)

The answer would be logical.