You don't show your banking app on the phone to police 
You tap the card you have used on their reader and it shows you have paid
There is NO personal information or phone involved
That does not exclude she was targeted or they were rude or she was the only one asked - we have no idea if her 'crime' is being from the global majority race 🤷♀️ - what we do know is that it looks fucking excessive for £1.75