Excuse me for butting in, but simply adding brake fluid is definitely not the right fix. No conscientious mechanic will top off brake fluid during other routine services such as oil changes, and we often get faulted for that.
If the brake fluid is low, and indeed adding some might make the red "Brake" warning light go off, (you didn't specify if it's the red light or the yellow "ABS" light), you have to ask "where did it go?" It's possible there is a leak and that must be addressed, but much more commonly the front disc brake pads are near the end of their life and a brake system inspection is in order.
As brake pads wear, front or rear, the pistons move out of the calipers they're in to take up the gap. That is how all disc brakes self-adjust. Brake fluid fills in behind those pistons and is why the fluid level drops in the reservoir. Almost all calipers today are designed well enough that they usually don't need to be rebuilt or replaced during a routine maintenance brake job. Instead, those pistons just get pushed back into the calipers to make room for the new, thicker pads. Doing that pushes the brake fluid back up into the reservoir so the fluid level goes back up. If an inexperienced / untrained mechanic filled the fluid previously, it's going to run over and make a mess. Spilled brake fluid eats paint too.
When an experienced mechanic sees low brake fluid level, he looks more closely at the front pads, especially when they're easy to see through spoked wheels, and for signs of wetness around steel lines, rubber flex hoses, and rear wheel cylinders. If he has your best interest at heart, he will recommend a brake system inspection. He also knows there's a real good chance he will be accused of trying to sell unneeded parts and services, so he might just keep his mouth shut, let you drive until a worn pad starts grinding on a rotor, and then you will spend more money when new rotors are needed. He won't be blamed, but it ends up costing you more in the long run.
Now that I've added my piece, I'll let you guys back to your conversation.
Wednesday, January 2nd, 2019 AT 6:55 PM