Bad Brake Caliper Causing RAV4 to Lose All Brakes?

My wife’s Rav4 had a bad master brake cylinder and a bad ABS actuator which were replaced by Toyota at 34,000 miles. When these went out, the brake pedal went to the floor and the car wouldn’t stop. Luckily we were in a parking lot and were able to get the car towed. Now 7 months later, I’m driving the car home and the brakes go out again. They were extremely spongey and it took a while for the car to fully stop. Toyota is saying she has a bad back brake caliper. Does this sound right? I’m having a hard time believing that one bad caliper would cause the car to lose all braking function. I didn’t hear any grinding or screeching after it happened but granted I only drove it about 10 more min after the brakes went out. Car is at 42,000 miles.