Red John is a marked man.  He has a three dotted tattoo on his left shoulder.  My question is, how did the P.I. know this? There are two possibilities here.

a) She was Red John's lover
b) She saw it at the Gym

I would go with option b personally.  If option b is correct, then Ray is more likely because we've seen footage of him working out.  It's very possible he wore a sleeveless shirt one day and that's how she noticed the tattoo.

Also, she recognized Red John at the door.  This makes me think the person who hired her was the one at the door.  She was sure she was working for visualize.  Therefore, Red John is a known affiliate of Visualize and very likely Ray Haffner.