Fuel gauge jumped then engine died on the freeway

My daughter has a 2009 Mazda rx8 last week on the freeway her fuel gauge started to go up and down and then her car just stopped we took it to the dealer they said it was the fuel pump and the battery, that was 1200 dollars. About week later the fuel gauge did it again but the car was driving ok, we took it back to the dealer and they said it could be the fuel sensor. I talked to a mechanic and he said when the fuel pump went out they should of changed the fuel sensor, is that or not.