Lizzie Saltzman, Legacies' Siphoner-vampire, was initially reluctant to use her magic at the beginning of the series for a reason she did not fully understand herself. Lizzie started out as a seemingly narcissistic and impulsive character with signs of mood swings and a codependent attachment to her twin sister, Josie. Lizzie's concern for her mental health increased as her behavior became more aggressive, causing a rift between her and Josie.
While solving the ongoing Vampire Diaries Merge issue could have motivated some of Lizzie's behavior, it became evident in Legacies season 2 that whatever caused Lizzie's erratic behavior was something that required treatment from healthcare professionals along with medication. While never outright confirmed, it was clear Lizzie always exhibited signs of bipolar disorder. Lizzie's inability to focus to maintain a stable mental state of clarity, along with her random mood swings, made her too afraid to practice magic which called for intentional concentration to use properly. Not being able to do so could spell harm for the or those around her. In short, Lizzie was afraid of herself and her power.
How Lizzie's Magic Might Have Hurt Others In Legacies
It has been demonstrated throughout being one of Legacies' Siphoners, Lizzie's mood swings and lack of focus could have led to dire consequences. In a manic state, she could unknowingly siphon too much power that could lead to her death, the death of the witch she siphoned, or an uncontrollably destructive use of magic.
What Lizzie Using Her Magic In Legacies Says About Her Character Growth
After Lizzie becomes a heretic–a Siphoner-vampire hybrid–it is revealed that she was also sired to Hope. That bond, however, was impressively severed when Lizzie saw a reflection of herself in Aurora, who Hope commanded Lizzie to torture. Lizzie's ability to sever her own sire bond relatively quickly has been noted as a result of her progress in her mental health journey throughout Legacies. Lizzie breaking her sire bond to Hope illustrated her growth in controlling her emotions and focusing her mind to be able to do something that took other vampires decades if not centuries to do.
Lizzie's confidence as a heretic grew hand in hand with her confidence to practice magic. It took her realizing she had the power to better manage her mental and emotional health, after she broke her sire bond, to gain the skills to properly and confidently perform magic. To be able to unapologetically be herself without fear of causing harm may have been Lizzie's biggest fear at first. Although Lizzie's exact behavioral or mental health concern was not made known, as Legacies' powerful heretic, Lizzie has shown that her greatest strength came from her witty, moody self and not her powers.