Only one app does not sync

3 weeks ago, I downloaded an app on my daughter's touch. Used it, works great.
Few days ago, I bought a touch and wanted to install the same app. Apparently it is not available for US customers anymore.
So I thought I'd be smart and just transfer it from her ipod to mine. The app is installed on her ipod and I can use it, but it's nowhere to be found on the device when it's time to transfer. I tried a phone browser, but it's the only app missing. How come ? How can it be installed, but can't be seen with a phone browser ?

Any idea ?

Thanks.

 

That's what's weird. I did all that. Authorized and Transfer.
It transfers everything else but that app.
If I am in iTunes and go under apps, right click to show in finder or explorer, I will see all the apps installed, but this one is not there.
It's hidden somewhere on the device.