hello
when the arrow light is on it means the overdrive is not engaged.
she will be getting poor gas mileage. but the high revs shouldnt hurt the motor. tell her to push the little button on the left side of the shifter and see if the arrow goes away and shifts into higher gear.
if not its usually the overdrive relay, but can be wiring or switch.
the relay lives behind the dash just under the center console a.c.vents.
remove glovebox and look to the left for a white cube relay. it can be reached with a screwdriver to pry up holder.
replace this first.
if arrow is still there post back for more info.
good luck
mike