Washer fluid in my brake reservoir?

Thank goodness it was washer fluid. I would use a turkey baster to suck out as much fluid as possible, then put in new, clean brake fluid. If you can remember how high the level was in the reservoir, fill it to the same level, no higher.

For the first issue, the level goes down in the reservoir as the front brake pads wear down. The pistons in the brake calipers work their way out to self-adjust, then brake fluid fills in behind them. Later, when a normal brake job is performed, we have to press the pistons back in to make room for the new, thicker brake pads. Doing so pushes the brake fluid back up into the reservoir and the level goes back to "full". If someone previously topped off the brake fluid, it will overflow and spill out making a mess. Brake fluid loves to eat paint too. This is why we never top off brake fluid during other routine services such as oil changes.

In your case, with the really low miles you listed, your brake pads will have almost no wear yet, so it's okay to fill the brake fluid to the "full" line.

The bigger issue has to do with what was added to the brake fluid. It can become an extremely expensive repair if a petroleum product is introduced, even a few drops. Engine oil, transmission fluid, power steering fluid, axle grease, and penetrating oil are not compatible with the rubber parts in the brake system. When that happens, all those parts with rubber that contact the brake fluid must be replaced, and the steel lines must be flushed and dried before any new parts are installed. If even one part is not replaced, the contamination will leach out of it and recontaminate the new fluid and new parts. These parts include front brake calipers, rear calipers or wheel cylinders, rubber flex hoses, master cylinder and reservoir, and all the valves in the system. If the vehicle has anti-lock brakes, as most of them do now, the hydraulic controller must be replaced too because it has rubber O-rings inside.

Washer fluid is not a petroleum product. It is designed to evaporate, but the brake hydraulic system is sealed, so that fluid will stay there. The bigger concern then is washer fluid has water in it. Water causes two problems. The first is corrosion of metal parts from the inside. The second is brake fluid boils at well over 400 degrees Fahrenheit. Water boils at around 212 degrees. Front brakes can get well over 200 degrees just from extended city driving. That heat migrates through the brake parts into the fluid where any water will boil and turn to vapor. That leads to one form of brake fade. Since the air can be compressed, it causes a low and soft brake pedal. To avoid that is why I want you to draw out as much fluid as possible from the reservoir. It's almost a certainty you'll get all of the washer fluid out.

Washer fluid is basically water and alcohol with a colorant added and in some cases a modified silicone (rain ex types) The brake fluid used in your car is a glycol based fluid, as such it absorbs water very readily. The alcohol in the washer fluid won't do much of anything. If you got it all out then I would probably take something like a turkey baster and draw out as much of the fluid in the reservoir as you can, then fill it with fresh DOT 4 brake fluid. Then drive it. Get some of the brake fluid test strips from the parts store and just test how much moisture it drew in. If it tests OK (which it should) then just plan on servicing the brakes as normal. Now if you had put oil in it you would not like the answer as that starts getting very expensive because you end up replacing pretty much every part in the braking system. In this case it shouldn't be a large issue. Although many shops would see dollar signs and start selling you a lot of parts, but likely not changing them.