Better she visits the toilet before leaving, rather than having to find one halfway to your destination.
When I suggest that I get 'Am I a child or something?'
30 mins into journey, 'We need to stop I need the toilet.'
Also, on the motorway;
Next services 13 miles and 43 miles - Silence*
Next services 5 miles and 35 miles - Silence*
Next services 1 mile and 31 miles - Silence*
Next services ahead - Silence*
Next services 29 miles - 'I really, desperately need to use the toilet. Can we stop?'
And whilst I'm at it why do women insist that the car audio entertainment system is switched off half an hour before your destination 'so that you can concentrate' then talk incessantly to you about inane crap that you will no doubt get tested on later?
*I say silence but actually mean the constant drone of who said what to whom and why they shouldn't have... rather than an indication that her bladder full level float switch is about to operate.
Edited to correct typo/bad maths