There are plenty of adult posters on MN who hate self scan and get flustered by it. It’s not a big reach to understand that a 14yo who has never shopped on her own to be a bit anxious about it.
I might be being a bit harsh here - but you sound very like a lot of parents I see around who are very comfortable in the early years of parenting but have no clue how to do older years. So just have more children that they can mother through the early years. With no empathy about the impact on their older children.
You say you’re close. I have a DD a little bit older. If at 14 she had been only comfortable going out with friends when parents were present I would have felt like here is something very wrong in her life arc and focussed on fixing that. That’s a level of anxiety that a 14yo shouldn’t have. They should be pushing boundaries (which is a whole other parenting challenge) and trying to find a path to adulthood. It’s part of growing up but absolutely needs parental support as they navigate that. They need you in their corner.
But you decided to have another child so she’s probably feeling like she’s even lower down the pecking order. And from what you’ve said the needs of the younger supplant the needs of the older. She’s asking for your help and you’re ignoring her and making her feel uncomfortable for even asking for it.
I have a very individual and independent 16 year old. I taught her to be that in spite of the restrictive lockdown rules. It’s your job as a parent. It doesn’t just happen by magic.
You can’t decide to unhave your latest baby, nor should you want to wish that. But you shouldn’t ignore the fact that you have a 14yo to parent at the same time. So you need to meet all of your children’s needs. Not just the baby’s. And yes I know that might sound overwhelming. But it needs to be done
Edited for rubbish typo :)