I'm imagining a kitchen table conversation (apologies if I mis-generation the names, I'm old and foreign):
Leah - You'll be going back to school soon, and you need a proper bra. I think it's time you had a clothes allowance and can choose your own, so we'll go to M&S and you can see how to do that.
Amy - But - what if anyone sees us? And will I have to talk to anyone? I don't like having to talk to people I don't know.
Leah - Don't worry, no-one will talk to you, it isn't that sort of shop, you just pick for yourself and pay
Amy - Promise?
Leah - promise.
next day
Leah - see, it's all here in this bit of the shop. When you're a bit taller you'll even be able to see over the display stands. Wait here for a sec while I find the the stuff for your age group.
Amy - Hurry up Mum, I don't like all these people knowing I need a bra.
Leah - (2 metres away, looks over her shoulder) Don't be silly, no-one will bother you . . . .
Peta - (6'2", looms over Amy) Hello, want some help?