Normally you have to see the course of treatment through to the end. It might be more difficult for a speedy fix in a coldwater tank because I know that normally when treating Ich in a tropical tank we are advised to turn the temp up slightly as this speeds up the whole process of the tiny white cysts to burst. You see, the medications for whitespot don't actually remove the white spot from the fish itself - it works by killing off the tiny Tomites that break out of the cyst and fall to the gravel.
The white cysts on the fish pop open much quicker at warmer temperatures and then once they have burst, the medication present in the tank water will kill off the Tomites so that the cycle cannot be repeated (otherwise the Tomites will latch onto another passing fish!).
When it's a coldwater fish, obviously this process will take longer for the white spots to pop and release the Tomites.
Tell your friend just to keep going with the meds for now. It might need a 2nd treatment - I'm not sure if it actaully tells you on the bottle of meds how to treat in coldwater conditions (i.e. for how long) but ask them to check.
Also, it might be an idea for your friend to keep an eye on their tank conditions before reintroducing new fish because whitespot is usually caused when the fish is stressed out and its immune system lowered. So something is causing the fish stress, whether it's water quality, sudden change of temperature (maybe not being allowed sufficient time to acclimatise to the tank water before being introduced into the tank) etc - sometimes they can even have caught the whitespot from the shop tank so it's always a good idea to check all the fish in a shop tank for signs of disease before buying any.
Hope that's helped - Athena
I can't believe it. 
