I have a friend who uses the bose headphones but when we go out to busy restaurants or other noisy places she tends to speak much to quiet for me to hear her...go figure the person without hearing loss ends up being the one having a hard time understanding!
I've got some passive noise isolating earbuds for concerts. I wore them to Gamescom and my wife kept asking me to speak up because I had the exact same problem your friend did. I could understand her speech perfectly, but felt like I became the person yelling and making all the noise.
I use 3M ClearE-A-R (UF01021), they're transparent and cost about 3€ for a reusable, washable pair on Amazon Germany. It does change the sound but I think that's inevitable (EDIT: for this price range, at least)
I would not say it's inevitable. As a musician, I use Elacin filters with custom moulds, and these are great. There is no noticeable change in the sound itself, you just hear the sound at lower volume and more clearly, without most of the echoes.
These are pricey though (around 200 EUR), but definitely cheaper than hearing loss.
I've also used he Etymotic "ETY Plugs" which are more expensive (about $12/pair) but are designed for flat frequency pass-through. They give moderate sound reduction without changing the sound.
These are the earplugs I used. I'm not sure if there are better or worse out there. The price point was low enough that I just bought them without a lot of research and they worked perfectly.
