OK, asking because if IABU I will give some money over.
We planned a cinema trip with friends, 2ad and 3 DC's (her DD's 6&8 and my DS 7 (yo))
Friend lives 10 minutes (max) walk from town so I said we'd meet at hers and we agreed to walk as car park for the length of time we would be there was £6 
Friend said go round bit earlier as her DC's wanted to play outside on new toys and DS could take roller blades.
So we turn up an hour half before time to leave and something happened between her 2 which left elder one screaming blue murder and having an hour long strop. Friend then said she wasn't going to go as her DD1 behaviour. I offered to take her DD2 but she said no - so I asked if she minded DS and I waiting at hers for the 20 minutes before we left? Not a problem she says.
Ten minutes later she announces she is getting ready to go but need to hurry as only has ten minutes now
. Her youngest DD then began to moan and whinge about walking and refusing to walk there. Using weather as an excuse. (was a little windy and had a quick shower half an hour before when they were outside). The whining went on and on and I said we had better get going or we wouldn't get there in time to book tickets and have a burger king as planned before the film started.
The stropping went on delaying my friend further until she said 'I'll have to drive now or we're going to be too late'. DS wanted to walk so I said we would leave and meet them there but her DD2 moaned again so DS said 'Oh I'll go in the car then if it keeps you quiet'

At this point I again mentioned cost of parking and that I couldn't afford it all but friend said driving was the only option and she had change on her. She said DS and I may as well go in the car with her as she'd have to.
So we go, book tickets, have burger king, get sweets and drink and go to film.
When we get out friend says if I wait with DC's she'll get the car park ticket (machine in different direction to car).
Then proceeded to mention the cost (£6) and how expensive it was for the rest of the afternoon.
I replied once 'I know that's why I said to walk'.
I get the feeling she wanted me to offer to pay some towards it - which at the time I didn't have enough cash on me as only took what I knew we'd need iyswim?
So been paid today - should I offer her half the cost or AIBU to think that as it was her and her DD's fault we went in the car she should stump up the charges? Not a major issue I'll admit but will do the right thing according to the MN jury!