I’m not really sure why she’s trying a 38N bra if her 34L fits better than her 34M... her underbust hasn’t changed so why is she looking for 38 bands? A 38N is 6 volume sizes bigger than a 34L.
Her actual measurements put her at around an LL cup but I don’t doubt she might be an N but on a 34 band, if she can’t get 34N bras she should be looking for 36MM and 38M bras (which hold the same volume) and altering the band down.
It doesn’t make any sense to getting bras that are bigger in both cup size and band size.
Why don’t any of the sizes she gives ever have double letters like UK sizing uses, is she buying US brands? A US M cup is only a UK J so if that is the case no wonder it doesn’t fit.