Is the brake fluid still clear or does it have a color to it? Does your roommate have any idea how much power steering fluid she added? If not much, it probably won't have damaged anything and flushing the brake system may be sufficient. I doubt that the power steering fluid contamination would cause brake calipers to lock up, but since you know a foreign fluid was added to the braking system, I'd again suggest replacing the brake hoses along with the brake system flush and bleed.
-Rod