While I would be sad to lose her, I can honestly say that I think she would be a terrific addition to your team. I understand that she is talking to you about joining your firm as an Account Executive. I always enjoy being assigned to projects with her because I know that she likes to take a collaborative approach and is very focused on accomplishing goals in a timely manner. She and I have worked together on the same team at XYZ Company for the last two years.
It is my pleasure to provide a reference for Lisa Neely. If a coworker asks you to write a letter of reference, it's important to emphasize that you are speaking about your personal experience with the individual rather than as an official company representative.