You might just want to fill the PS reservior and bleed the rack. I know what you are talking about with the foamy fluid... kinda looks like a freshly poured Guiness.
My PS system was completely disassembled for over a month as I had the car back and forth getting the engine compartment painted. Upon reinstallation of the engine, I had to add/bleed the system 2 or three times before the fluid looked like it should.
To bleed the rack, jack & support the front end off the ground a few inches. Add fluid, start engine and turn steering wheel left and right all the way until it stops several times. Shut engine down and check fluid level. Repeat if necessary.