Yeah but shes probably only using them because they are there... I have lots of friends who love my headphones but would never drop that kind of cash on them.
To them the thought is insane...
I bought my gf a pair of ESW9... wished she used them more lol. At least there are decent headphones at her place though when we study together.
Was a pretty bad gift idea though (wasn't aware at the time) but her hearing is not super good as it turns out. Huge history of ear infections as a kid due to abnormal canals... stuff that drives me crazy she doesn't even notice. Oh well... its the thought that counts at least... (i hope!
If you haven't been with her a long time maybe just offer her a really good price and tell her straight up: Look I was planning on selling these to get X, but you seem to really like them so blah blah. Still iffy and depends on her personality, but if she knows people are willing to pay X second hand and be happy she will hopefully realize the value.
It is always iffy when you bring money into a relationship though... the barter system tends to work better.