I would like to field that issue here and now. I would like you to understand how Nyssa was beaten and abused for as long as she can remember even still she is mocked for who she is and how she is. Without a parent she was never taught how to deal with emotions and stuff properly. SHE HAS NO IDEA HOW TO DEAL WITH EMOTIONS. That and the bad past made her emotionally unstable to say the least something that stays hidden behind her aggressive nature. That makes her relationship with Ardor and Jess weird to her anyway and she can't understand it or the way she feels.
THEN ADD RESPAWNING Nyssa can respawn as part of her "Shoura" title and she will do until Malgroth is dead. So since that happened she has gotten into the habit of cutting herself when she has lapses in her 'stability'. It's not uncommon to find her hidden away stabbing at her hands and arms calling herself a "monster" or "freak" She just feels worse with the ability to respawn and like she wants to die but she can't.))
((I imagine it went relatively unnoticed because of the whole "Respawning back as normal" thing (Apart from death scars if they're bad enough) until she is 18 when she starts getting really depressed sometimes and actually kills herself a couple of times (Only to respawn) is when th recovery process truly starts...))