All you can do is laugh. . .

Ava: I have to go potty.  I have to go potty.

Parents:  We're almost home, can you wait?

Ava:  Yes.
Two seconds later . .
Ava:  I have to go potty.  I have to go potty!

So this goes on for a bit until Ava's pitch reaches intolerable levels.  Parents determine that a stop in necessary and pull off the highway and down a side road a bit so Ava can get out and go.  And it's raining.  Awesome.

The situation is remedied and the car turns around and heads back to the highway.

Ava:  What are we doing?

Parents:  Turning around.

Ava:  But I wanted to go home!  Why did we stop?

Parents:  (one . . .two. . . three . . .)  We had to pull over so you could go to the bathroom.

Ava:  What are you talking about?  Why aren't we home yet?!!!

Father to Mother:  Breathe in, breathe out, breathe in, now out . . .