Why do the tail lights work but the brake lights won't?

My grandmother has a 1990 Infinite. She's had it about 8 mos. and has only been able to drive it twice because her brake lights don't work it's the weirdest thing. When she first got the car everything worked fine. Then one day she got stuck in her yard. We live in Fl. and it was right after the hurricanes flooded us, so she got stuck deep, the body of the car was on the ground the tire was buried. When we got the car out the brake lights wouldn't go off, unless you hit the brakes then they went off. My husband put a stick to hold the brake down til someone could look at it the next day. His dad was a mechanic but he's completely car illiterate!) The next day we took the stick off the brake and they stayed off but would not come back on. The tail lights work, and I've changed the fuses the bulbs and the brake lights still won't work. I'm tired of seeing her with no way to go since the only one who knows anything about cars is my Uncle and he's been too busy for the last 7 mos. to come fix them for his mother. So if anyone can tell me how to fix it or any ideas I'd be so grateful. And thanks for taking the time to read all of this even if you can't help, I just wanted to be as specific as possible.