Yes, she does need something to do, you really should be doing something with her on a daily basis. Why not take her out for trail rides? Most horses do best with a regular schedule and something to do. If she was in work before and now she isn't doing anything at all, that could be a very good reason for her to be pacing the fence line to burn off some energy.
I still think that horses really shouldn't be expected to live alone all of their lives.
If you do get another horse, you will need to teach your horse how to behave away from other horses. This horse has never been taught how by the sound of it.