Cadillac Repair: 91 deville, light glows, faulty sensor

Question
I changed the brake pads recently for my granddaughter on her deville. I got finished and top off the reservoir. She drove to school and called to let me know that the brake light came on. Could you give me a hint as to why other than low fluid?   Thanks

Answer
IS or HAS the CHECK ENGINE light ever illuminated while driving the vehicle and or has any other lights illuminated or any messages from the message display center ?.

Ask her to WATCH the brake light as she engages the emergency brake and see if the brake light glows BRIGHTER.

If NOT, It could be just a faulty sensor.