Ask HN: Determining compensation package based on consulting rate

A friend of mine is currently working as a consultant and is billing per hour. The issue is that the work comes and goes and therefore is considering joining consulting firms full time as an employee so she doesn't have to do marketing and sales. How does she determine what the compensation package should look like and what is the best way to negotiate/leverage given that she is currently engaged on a project working directly for a client similar to other clients of the consulting firm?