Your daughter will have to learn to stand up for herself more than she expected to at her age. Bullies like to prey on the apparently weak and defenseless - children losing a parent fit right into that category.
She has to know that being willing to speak up for herself, and being willing to ask for help when things are beyond her control are good skills to develop and use. Bullies can only be dealt with by standing up to them and forcing them to back down. Any type of appeasement action against a bully only encourages them.
Be careful of approved authority figures as well. They can act as bullies as well, just with tacit approval that people find difficult to challenge because they are the approved authority.