The bottom line is that yea, it is easy to make a mistake like this and it happens all of the time with fish like Bala (silver) shark, ID sharks, tinfoil barbs, plecos, etc...etc...etc...
Those fish aren't even in the same league, with the exception of the ID shark which arguably can reach 3 feet all those fish have a maximum size of around 14 inches and can be housed in a large off the shelf tank, they are also fairly cheap fish to buy so don't provoke much thought when purchasing. Silver arowana on the other hand will definitely grow to over 2 feet long and are reasonably expensive fish, i don't know about in the US but in England you don't expect change from £40 (about $80) and I'm pretty sure most people don't just part with that amount of cash for a fish without knowing something about it.
I am not discouraging her in her attempts to re home her fish but am simply stating facts, again things may be different in the US but here public aquariums and zoo's will not take in your over grown fish, there was even an article on it in PFK last year where they asked all the big aquariums around the country if they take in various fish, the answers were mainly no. You only have to take a look on aquarists classifieds to see how many people are trying to re home arowana's and other tank busting fish or take a look around the sump tanks of shops up and down the country and see how many large fish are living out their lives on the bottom row in tanks they can barely turn in to see that 99% of these fish don't get re homed simply because 99% of people can't house them.
I in no way believe that Americans know nothing but there are certain forums which shall remain nameless where the average member is a young American with little regard to the housing of the fish as long as they look "cool", these same people also think its cool to feed mice to predatory fish and take videos of their fish in undersized tanks eating goldfish, maybe that's acceptable in the states but its looked down on here, social differences maybe.
From what you are saying you think we should sugar coat our replies and tell people that its OK to keep a fish that gets bigger than some dogs in a tank that's barely large enough to keep a 12" fish in and that its OK because someone with a big tank will come and bail you out. Sorry but this is the real world and when you make a mistake you take the flack for it and have to take the action to rectify the mistake, if you buy big fish you have to be prepared to buy a big tank.
I'll overlook the fact you posted a link to your forum (which i have removed) and not take any action for it as i believe you may have jumped in to defend someone without actually thinking it out, maybe i'm wrong but i hope i'm not as i have always thought of you as a decent responsible hobiest.