i had something like this recently - my hair's about half way down my back and i emphasised to my hairdresser that i wanted to keep it long. what she did was put a heavy short layer in the top and leave the rest long, kind of half and half, i've seen a few fashionable types with something similar lately so it must be current. anyway, it looked great down, but meant i couldn't actually put it back in a bun the way i normally do, the top layer was too short. and it looked like crap in a plait cos all the short ends stuck out and there wasn't enough hair at the bottom. i wear my hair up 90% of the time so this was a big deal.
i actually made an appointment to go back and have it all cut short. i'm really not precious about my hair and i'm happy to experiment with cut colour, before i grew it long i'd never have the same style twice. but to cut long hair short is a decision that i should have made, i shouldn't have it forced on me by a hairdresser.
in the end i spent a bit of time on youtube and found a couple of ways to put it up that would do while i was waiting for the layers to grow a bit longer (this was about 6 months ago, it's just about long enough to go back in a bun now, or i use clips). i really didn't want to have it all cut off. and it did look a lot better down, so i wear it down more often now.
sorry for epic tale. i would suggest a) playing around with it and seeing if she can find new ways to wear it, and failing that b) go back to hairdressers and insist they fix it. personally i think short hair looks much more stylish than long, and i always got loads of compliments when i had different short cuts. it's also much more fashionable to go short. do they still have those hairstyle mags? or the web equivalent, look at it as a fresh new start.
but make sure you get it for free and make sure the hairdresser doesn't mess it up, choose something suitable for her face shape/hair type and take a picture in to show the hairdresser.