"I'll drive you to the MRT, then," her father said.
After saying goodbye to her mother and promising to come back soon,
Naomi got into her father's car, and drove off to the main road with
him.
What I want to say is: "She got into the car and then her father drove off to the main road." I'm not very sure but I think the with him implies that her father was the one driving. Or it reads as if Naomi is the one driving the car? (Or drove off actually means left to the place and started heading to X so it isn't actually a problem?)
Best Answer
Yes, with that sentence, I would understand that it was Naomi who was driving. Since the subject of your sentence is Naomi, any verbs will be assumed to be her actions.
The easiest way around this would be to simply say
The they removes ambiguity and you don't really need off, drove will do. To drive off brings to mind driving into the sunset, going away with no specific destination in mind. It is rarely1 used when a destination is specified.
However, as @TrevorD points out, this sounds as if they are driving towards the main road. If you want them to drive away on the big road you could write:
This brings to mind an image of their driving away into the distance down the big road.
1It is actually a relatively common idiom in some parts of the UK where you will hear I drove off to the store but I would be surprised to see it written.