It’s so bad that my fiancée has some bras that say she’s a B cup and others that says she’s a D cup. In order to go bra shopping, you have to actually try them on to find out if they fit.
If I had to try on underwear to see if they fit, I might not bother with underwear at all!
Have her go and get fitted. Many women don’t know what their band/cup size really is.
Also, IMO, women’s pant sizes are where the real absurdity in sizes is.
Not much help to know what cup size you are if the bra companies are only pretending to be standardized
Agree on all points! When I was had my first grownup job I was trying to build up my wardrobe and found a pair of jeans that fit and felt great. Size 3. I went back after another paycheck to get an identical third pair and when I got home, they were practically falling off of me. I had to exchange them for a 1, which was still larger than the size 3s from just a month or two earlier.
But a fitted bra? One of my best purchases ever. Getting in the right size resolved about 70% of my chronic back pain. Fit is different between bra types but decent brands’ sizes are standardized, regardless what OP says.