Aunt was left unattended and fell after Brain Surgery

My aunt recently underwent brain surgery to remove a tumor about a week ago. She currently has significant mobility issues and has required constant attendance since the procedure. ​A serious incident occurred during a recent session with a speech therapist... My aunt requested to use the bathroom. The therapist escorted her to the bedside bathroom while my grandmother and two young cousins were in the room. The therapist then exited the bathroom, closed the door, and left my aunt completely unattended, despite knowing her mobility limitations and recent surgery. My aunt subsequently fell to the floor, hitting her head and sustaining a massive bruise just days after major brain surgery. ​Although a scan did not immediately reveal new internal damage, my aunt is now suffering from a severe, persistent headache. My family is determined to pursue a lawsuit against the hospital for medical malpractice and neglect. ​We have never been involved in a lawsuit before. I am currently reaching out to attorneys, but I need to know if there is a specific process or set of immediate steps we should be following right now to build the strongest possible case. ​What is the correct process for initiating a medical malpractice lawsuit, and are there any critical steps we should take immediately while contacting lawyers?

​TL;DR ​Aunt with mobility issues after brain surgery was left unattended by a hospital speech therapist in the bathroom, fell, and hit her head, resulting in a severe headache. We believe this is medical malpractice and are looking for advice on the proper process and immediate steps for starting a lawsuit against the hospital. ​