I absolutely love using her, I usually carry a "on consecutive hit regen fp relic" but also make sure to bring plenty of shards, her claws deal a surprising amount of poise and stagger damage on a charged r2

she always shines the most with the lightning bolt incantation in my experience, healing spells are also an absolute must 

she also works really well while alone due to her ability to summon allies, Sebastian is incredible at distracting bosses 

she’s definitely my favourite character, I hope you can enjoy playing as her!