(Been a while since I saw the movie.) When the wife jets off the supply shuttle (?) at Mars after her husband, she has to stop just out of reach of her husband. Distance would not matter. All she would need is to go faster than her husband, which she was.
She also set her fuel warning at 1/2. This is wrong. Assuming that she massed as much as her husband she could only use 1/4 tank of fuel to launch, 1/4 to slow down, and 1/2 to accelerate her and her husband back to the shuttle. They could impact the shuttle to stop or let the other astronauts catch them.