Again, why is there a need for a stick? It's like parents who can't raise their children without corporal punishment, saying it's all done out of compassion. I don't think it is. Compassion doesn't rise from hitting, screaming, pushing. In the same vein, I do not think it is proper to have a compassion knife, gently pricking someone to make them see the fragility of their body. Or something. Is that skillful means? In my humble opinion, no.
I'm not saying that it's always appropriate, but I would be disinclined to say that, as an example, a carefully considered strike from a compassion stick is inherently violent or angry in nature.
If she asked for it herself, then, perhaps that is another question altogether?
Likewise, perhaps some are motivated by more aggressive techniques more than a similar soft technique (I'm thinking of one specific friend who, while she was trying to lose weight, asked her trainer to shout insults and obscenities at her. It worked.).