Why does my car stall out of no where?

So after my gf drove through a flooded street and the car idled or lost dash lightning like if it was going to shut down but it didn’t . Weeks after it stalled on her while she was driving (once) then another time while she was at a stop sign. ALSO. It made a buzzing sound while starting it..my gues was (ignition switch electrical part. Or start up relay..So I took it to the dealer and had it diagnosed ( supposedly) and they said it was the ignition switch connector so I paid for it (arm and a leg) and serviced it. And just today gauges and radio dimmed and died.. completely shut off.. after I waited and went to turn the ac on all the lights went on. So I played with the ac on and off and it wanted to die… I REALLY NEED HELP CAUSE I AM DRIVING FROM LOUISIANA TO CALIFORNIA AND DONT WANNA GET STRANDED IN THE DESERT .. PLEASE HELP VERY MUCH APPRECIATED..THANK YOU