The mum thinks I'm being petty, but I don't want to drive her kid

I think that I would reiterate to the mother that I'd said I wouldn't give her 7 year old a lift ever again, but having thought about it I realise that over the last year she might have matured a bit and be able to sit quietly in the car. So you'd like the mother's assurance that this will be the case? If the mother says yes, she will sit quietly, you say that's great, but if there are any outbursts I'm afraid that I will have to stop the car and you and your younger daughter can walk home as it's not safe for me to drive with arguments going on. Good luck!

I cannot understand why the mother sent BOTH girls to their rooms - why punish older daughter for younger's bad behaviour??
How about saying you will do a trial journey IF older daughter sits in front and younger sits in back with mother and entertains herself, making sure she sits still, behaves and does NOT distract you or be horrible to anyone and shows you that she can behave without her mother indulging her - which would give you a way back for an emergency in the future??
Good luck

Nah. Why bother? The kid getting places isn't OPs problem.

Or how about....not?

It's not OPs problem how the children get around.

Yanbu. The mum needs to stop asking for lifts and sort her spoilt brat of a child out. Obviously isn't parenting properly if its still a problem a entire year later.

The 'friend' called the op petty?

All those that are saying that they would give the 7 year old another chance, why would you, when the mother is being obnoxious and calling the op names?

Seriously?

That is not the action of someone being friendly.

I would offer a lift if mum is in the car but be clear she is responsible for her DDs behaviour

I think a car ban on a child who will not stop shouting while someone is driving is perfectly reasonable, never mind any of the other behaviour. I wouldn't take this child anywhere again for safety reasons, apart from anything else.
I do think driving one child but not the other is creating a division, though. Although it's not fair on the older child, a blanket 'I will not drive your children anywhere any more' would be more straightforward.

i dont think you can do this personally
the issue is her behaviour towards her sister
give her another chance

Like others, I was the older sibling at the mercy of a younger sibling.

We both go reprimanded if she had done anything, I was told to put up with her behaviour and abuse. She had an explosive temper and a cruel streak. The day I was diagnosed with anorexia she told me I didn't need to starve myself, if I didn't want to be fat I just needed to exercise more. My mum sat back and said nothing.

There were times when we were out in public where if I told her off for her behaviour and actions towards me and my mum would tell me off as highlighting my sisters behaviours might make others think she's a bad mum.

I learnt very early on that my needs don't matter, be the voice that supports the 14 yo

I cannot understand why the mother sent BOTH girls to their rooms - why punish older daughter for younger's bad behaviour??

The thinking is the older daughter has to also be punished to show the younger daughter she is being treated fairly. The older daughter by merely existing winds her sister up so needs to be punished equally.

Only punishing the younger daughter would lead to an epic tantrum the parents don’t know how to manage. So they resort to relying on the elder daughter to be the bigger person and the “good girl” who won’t kick up a fuss.

The patterns are already embedded and will carry through their adult lives or until the older daughter says no and means it.

There are many older daughters who recognise this scenario.

of course the OP can do it! Why do you think she can't?

the OP has said that she knows there is no change in either the behaviour ir the dynamic.

Why are you friends with someone who treats their 14 year old as a nuisance? What redeeming features can this woman possibly have that makes up for that?

dont be a hero
she is your friend

Why is OP responsible for getting the family anywhere?

She owes them NOTHING.

Stick to your guns you did the right thing calling this behaviour out .. at 7 she sounds like a brat and the older sister unfairly treated its not on.
Id do the same my answer would be no ill take 14yr old anywhere but not 7 yr old as she was awful in your car.

@AvacadoChic

This.

Mum, and sadly younger child, sound like bullies.

The 7 year-old child never apologized, did she? That is one of the reasons I'm glad you are sticking to what you said. I doubt she has changed because she has no reason to change. She has at least her mother wrapped around her little finger.

As for the older girl, she hasn't had a chance to be outgoing since her sister hogs the limelight and the attention.
Since she doesn't really have anyone on her side, she will find someone to give her attention and a way to forget her pain. If she doesn't, she'll just keep making herself smaller and smaller while her sister continues to act to big for her britches, as my Mom used to say.

I have seen this dynamic played out time and time again. Its so damaging for the scape goat and doesnt end to well for the golden child. The 7 yr old sounds horrible to be frank. Stick to your boundary. Other incidents will happen and maybe the parents will see how unfair their behaviour is. 1 friend of mine had a beautiful water colour done of the youngest golden child running across a beach. It was done from a photo of both children the eldest was simply erased. They even had the original very art photo framed it was really shocking.