I disagree with you can never change to much, maybe if they are doing water only but if they gravel vac every day they can kill their bio bed and she has a cartridge filter that really doesn't hold as much bb as say a aquaclear with ceramics or matrix so she could be causing her tank to cycle constantly because of all the gravel vac's killing the bio bed (substrate).
She new so I'm trying to keep it simple and not frustrate her from confusion lol, yes technically you can do water changes everyday as long as you're not vacuuming the gravel every day, your filter holds 80% of your beneficial bacteria your gravel holds 20% (approx )
So keep doing 25% every night before you do your dose of rid ich, as coralbandit said lights off as I mentioned way back in the post do the treatment before you then your lights off for the night, don't get frustrated as fish keeping can be frustrating you just have to read, ask people, etc etc.
I do agree it can be done though, but I wouldn't recommended doing it for someone who is new.
