How to enable legal assistants to receive email notifications for the case?

In order to trigger the notifications, there are two prerequisites
1. She enables notifications in her account setting
2. She is assigned to the cases

Step by Step guide
Step 1. Create an user account for her(if she's your long-term/permanent staff, set her account role as Attorney)
Step 2. Add her as the assignee for cases that need her attention. (Go to the case, click Checklist, Assigned Attorney/Paralegal)

Step 3. She needs to enable the Notification settings in the Account Setting