Put power steering fluid in brake reservoir

That is really bad news, but you have the short time period on your side. Absolutely do not bleed any fluid at the wheels. Petroleum products like power steering fluid, engine oil, transmission fluid, axle grease, and penetrating oil will eat all the rubber parts that contact brake fluid. There's a good chance the power steering fluid didn't make its way down the lines yet.

I would get the master cylinder off the car and replace it, but first, with the lines disconnected, go to each front wheel and use a large flat-blade screwdriver to pry the pistons back into the calipers. They should move fairly easily a good 1/8" to as much as 1/4" That will push brake fluid up out of the lines and wash any power steering fluid out with it.

Now you can connect the steel lines to the master cylinder. That new one should be bench-bled first, then once it is installed, you still do not need to bleed at the wheels. Loosen the steel lines and have a helper slowly push the brake pedal halfway to the floor. That should take fifteen to twenty seconds. You'll see air bubbles squirt out by the line nuts. Snug the nuts, then have your helper release the pedal. Open the lines and do that again, and if you still see bubbles, do it a third time. With the nuts tight, stroke the brake pedal a few times just a quarter way to the floor. Push down very slowly, then release it very quickly. By pushing slowly, you'll push brake fluid down the lines and give any air bubbles time to float back up. By releasing quickly, the fluid rushing back will wash any remaining air bubbles into the reservoir.

Be sure the new master cylinder comes with new caps with rubber bladder seals under them. That rubber will also be attacked by power steering fluid. If the power steering fluid had been in there for a day or more, the entire hydraulic system would need to be replaced. That includes the calipers, wheel cylinders, combination valve, and four rubber flex hoses. If the car has anti-lock brakes, that hydraulic controller must also be replaced. That gets to be a real expensive repair. Any part that has rubber o-rings or seals must be replaced.

Let me know how it goes after a few weeks. This is the first time I ran into this in such a short time frame. The first one I was involved with was a 1959 Edsel I bought at an auction. The previous owner put automatic transmission fluid in the master cylinder to swell the seals. That made the brakes work great, for a few days. After that, it took a full tank of gas to drive 55 miles to an old car show, and halfway back home. I coasted into a gas station parking lot and missed the pump by ten feet. I couldn't even push the car that far by hand due to the locked brake. Got home and once on the granite driveway, the right front tire skidded all the way to the house. That one only needed a master cylinder, four wheel cylinders, three rubber hoses, and flushing the lines.

Also ran into this on two customer cars, one done intentionally just before they sold it to my customer, and one supposedly done accidentally, "by someone else". The first one was an old Ford station wagon that ended up going to the junkyard. Second one was a newer car. The repair bill was quite high, but that car was worth saving.

Years later when I was teaching, I did a demonstration each year where I put rubber wheel cylinder lip seals into two beakers with fresh clean brake fluid. In one of them I put one drop of engine oil or power steering fluid, then we let them both sit for a week. After that week, the contaminated seal was mushy and had grown about 20 percent larger. In the master cylinder, those lip seals grow past the fluid return ports and blocks them. That keeps the brake fluid in the lines under pressure, and that keeps the brakes from releasing. As they heat up the brake fluid gets hot and expands, and that applies the brakes even harder. That's what happened to my Edsel.

The only way to solve that is to remove everything that has rubber parts that contact the brake fluid, flush and dry the steel lines, then install new rubber parts. If any rubber part is overlooked, the contamination will leach out of it and recontaminate the new fluid and parts. When the car has anti-lock brakes, the hydraulic controller must be replaced too because it has rubber o-ring seals. That can turn the repair into more than a $2,000.00 ordeal, and that is more than some cars are worth

You may have been lucky, but a professional would never stake his reputation or his customer's life on a partial repair. This is one time we would never want to cut corners, even if it means the car isn't worth repairing. You haven't lived yet until you fly up behind a car stopped at a red light and your brake pedal goes to the floor. With less than a second to think what to do, I stuffed my minivan into a snow bank with that other car 18" to my left and a light pole 12" to my right. Mine was caused by a rusted-out brake line that decided to let go at the most inopportune time.