Actually - can anyone suggest somewhere better for measuring teenage girls for bras?
I once worked for an online lingerie retailer and tested the bra fitting services of high street retailers.
M&S was the worst and a hard no as they a) used the old method from 70 years ago which was appropriate for the materials used back then (underbust measurement + 4 inches)
and b) didn't fit me into the bra I needed, but into the sizes they had in store.
Excellent alternatives I found locally
John Lewis
Debenhams
Jenners
House of Fraser's
Bravissimo
&
most independent retailers
My best advice for all women is to learn how to measure properly yourself, teach it to your daughter, then teach her the signs of a bra that fits and one that doesn't.
Once you've taken your own measurements, if you have the time, go to one of these retailers, have them measure you and compare with your own measurements. Then visit a few more, keep notes (take photos of the bra labels they bring you that look best so you remember).
If you're at a good shop, they will explain what to look out for in the perfect bra. Armed with that knowledge, take your daughter to whoever did it best. Note the bra size they recommend and if you cannot find an affordable bra at that shop, try own brands.
They don't all fit the same way btw, some brands give you a particular shape that you may or may not like and that may or may not suit your particular shape and needs.
I have been trying for ten years for instance and cannot find any Debenhams own brand bra to fit me. Not one. Not ever. They are pretty, the fabrics feel nice and the price is good. But they just don't sit right for me, not even if I try adjacent sizes to my own.
P.S. If like me, you make the change from M&S, you may not want to believe the others are giving you the right size.
M&S had me in a 38D, I now wear either a 32G or a 34FF depending on my weight and comfort levels. The M&S ones used to slide up my back by the afternoon and sag in front, the others stay put all day, but can start feeling uncomfortable by the evening.