My brakes have become suddenly soft, but I can still stop.

Then the brakes seemed to get a lil bit better, but the car started overheating. I replaced the fan clutch, and solved the overheating but she's started to brake erratically... Feels like she's pulling to one side yet she brakes straight.

I can't find any leaks in the vacum lines, and she has new brakes all around. The master cylinder looks good to me, no change in the brake fluid.

Could this have been a temporary problem from air in the lines? Or possible water in the brake fluid?

It has been extremely cold here in the last week so I was thinking it could be water freezing in the fluid, but she brakes the same when it warms up in the day.