Steering wheel shakes when I brake from highway speed

A shake through the steering wheel that you also feel as a pulse in the pedal usually points to the front brakes, most often rotors with uneven thickness or pad material deposits on them. People call that "warped rotors", although true warping is less common than uneven wear.

Other things can feel similar: worn suspension or steering parts, a wheel that was not torqued evenly after a tire service, or a tire with a balance problem. Those usually show up while driving as well, not only when braking.

Because this is a braking issue, we would not guess remotely. Have the front pads and rotors measured for thickness and runout, and have the wheel lug nuts checked for correct torque. If the pads are original at 48,000 miles they may also be getting low, so it is worth inspecting soon rather than waiting.