I knew a kid that was mean to dogs, literally screamed in their ears and beat them with sticks... he ended up with 37 stitches and facial scars he will have to live with for the rest of his life. The dog that did it went to a second chance ranch and is doing wonderful. The boy... probably wont abuse animals again.
Just saying, it might not be a betta fish, but what goes around comes around. Having a "mental issue" is just an excuse to get what you want or that your a damn brat, especially if its an anger issue. A good ass kicking usually solves it pretty well.
Well...I had no idea that my "mental issue" of ADHD is better treated by a dog bite to the face than medication. I'll be sure to ask my doctor if I should change my treatment from a daily pill to a vicious dog since I never grew out of all the symptoms. Maybe the vicious dog will bite away the last bits of "excuse" left in me.
From my experience in a doctors office, only about 1 in 7 have actual issues that deserve medication. Otherwise its a quick and easy fix for doctors to just medicate kids rather than fix the actual problems they may be having whether its family or socially related.
Back to the fish, I would rather not go on a tangent about overly medicated kids and vaccines.
Move the fish to your room, leave the tank, see how long it takes your folks to notice.
I too don't want to go on a tangent about medicated kids and vaccines. Especially since I feel very passionately about both topics and could go on forever defending the validity of medications for people of all ages and vaccines.
However, you can't do the equivalent of throwing a match into a forest and then call the resulting fire a tangent. I would look the other way if you at least gave good advice that could help the OP, but your suggestion will just get her in trouble and increase her stress. If her parents want the fish to stay where it is because they like it there, it's a decoration to them. Once the OP finds out how long it takes her parents to notice, she will also find out how much time she has to put the fish right back where it was. That puts her 2 steps backwards.
My advice to the OP is two fold:
1) Follow Aus's advice and get her parents to realize that what is happening is bullying and should not be toleranted. Just because the threats are aimed at a fish instead of a puppy doesn't mean the threats aren't a form of emotional abuse.
2) Get her parents to realize just how unstable the sister is so she can get proper treatment. There is more than one pill. If the first medication had bad side effects, go back to the doctor and try something else. There are also ways to control mental health issues besides medication. Maybe the answer is therapy or behavior councling. Either way, the OP's sister needs professional help.
I usually don't play abuse or doctor card when offering advice, but the sister's behavior would alarm me even if she was threatening to damage dolls instead of kill fish. The parents are missing major red flags.