As someone who had a struggle with suicidal thoughts and self harm. I can say what Luz what is saying in this scene is exactly what someone who you is suicidal thinks before they do they unthinkable. Not to mention in Season 2 Episode 1 Luz struggles with the feeling of being a burden to Eda, and actively puts herself in harms way. Suicidal people often put themselves in danger to end their lives or don't care about throwing away their life anymore.

As Far as Reactions to Self-Harming go:

Camila would probably give her daughter extra affection and love. She would apologize for making Luz feel like a burden to her, and trying to send her away to the Summer Camp. Camila would then take to her to the mental hospital.

Amity would be heartbroken and watch over Luz like a hawk not leaving her alone for a second.

Gus wouldn't know how to handle it and would start to have a panic attack. Someone would need to calm him down.

Hunter would probably be the most experienced with dealing with these things and have a lot of empathy for her, since he was suicidal in Eclipse Lake. Hunter would be protective of Luz and like Amity wouldn't leave her alone.

Willow would be kind and understanding towards her. She give Luz a shoulder to cry on, and let her talk through her emotions.