It was mostly a sincere comment, with a bit of sick humor. Seriously, though, ammonia & nitrite poisoning are going to have the fish struggling to stay alive, and they won't have a lot of energy to be nipping at each other.
The answer to your real question, though, is that it depends on you. If it were me, I would say something like this:
"You know, I'm concerned about the fish in your fish tank. The tank isn't cycled, and that means they are probably all going to die in the next few days unless we do something quick. I can help by bringing in some populated filter material. "
"Unfortunately, that's really not the only problem. The fish aren't right for the tank. There is a pretty well established rule of thumb for the number & size of fish in tanks."
"By the way, certain fish really shouldn't be kept together. When the fish are all feeling good and used to their tank, the green terror is going to eat them all."
"You know, keeping fish is a lot more involved than it seems. I've been doing it for a while now, and made some mistakes along the way, but I really didn't get going right until I started reading up on the subject on the Internet."
OTOH, sadly enough, this is nearly always a self correcting problem. At the current rate, there's going to be a tank full of dead fish in a few days, if it hasn't already started.
I think I might tell her tomorrow that the setup that she has might not work. It makes me sick just to see all these fish in such a small tank.
