Tamagotchi killing clubs? *laugh* How immature. I honestly don't think the Tama really has anything to do with this whole situation.
Sit down and talk to her and ask her straighfoward on why she is doing this. I had a friend that started ripping Barbie dolls apart because he went out with a girl that look like her, and she humiliated him in front of his school...by accident. All he needed to do was to confront her and make up, but instead he wasted his valuable money on plastic dolls and a hammer.
Now you friend is depressed for one (or more) of the following reasons:
1. She probrably named the Tama after a family member, or somebody special in her life.
2. She got into an argument with somebody she loves and the Tama died around that time, and she got mad and thought that killing Tamas could heal the pain.
3. She's a l*sb**n (hey, people that hide their feelings do that)
or
4. She's craving attention.
BTW, is she physically killing the Tamas (like breaking it) or just the little characters on the screen?
I cried when my P1 Maskutchi died. But I didn't do anything irrational like that...besides, I was running a Mesu and Osu at the time aswell.
Healing yourself is only step 1: everything else is determined by that.