As far as I know, the website (Jetnet) where we access the non-rev travel planner is available only to employees. I know a number of employees who give their login information to their spouse/partner/casual observer, but in most corporations (and I spent over 20 years in the Information Technology fields) giving your logon info to anyone, including another employee, is a termination offense.
Considering what happened at DFW recently, I don't think the company would be in a forgiving mood. What happened? A gate agent posted the passcode for accessing all the DFW AA jetbridges on Facebook. The gate passcodes had to be changed at every AA gate in DFW. A definite no-no. The TSA and the FAA are investigating from what I heard. I hope that employee has a backup plan for long-term employment.
My guess is that the employee who has designated you as their registered companion will still have to book your travel for you. But, I wouldn't swear to that. There have been a lot of changes in the travel system policies over the past year or two. Your companion should find out the answer to your question, if for no other reason...their own peace of mind.