Jessica and Rebecca are old friends and childhood playmates, though only because Jessica's family has worked for Rebecca's for generations. A fact that Jessica tries to hide so she can portray herself as a rich girl.
At first, Jessica thought of Ash as just another person, and may have looked down on him for his lack of a Pal prior to Echo's birth. This changed when Ash saved her life, and revealed he was her crush the Silver Knight.
Ever since then, she's been very attracted to him and has attempted to seduce due to her intentions of bearing his child and becoming a noble. While her reasons for liking him were vain, she slowly developed genuine feelings after seeing his kinder side and willingness to risk his life to help others.
Jessica didn't think much of Silvia, in spite of her being a princess which gives her a higher status but she did protect her from Avdocha's terrorist subterfuge. This act surprised Silvia who tried her best to save her before she worried for Jessica.
Ever since, the two have grown to respect her and get along better even if Jessica also sees Silvia as a rival for Ash's affections. Silvia is also one of the few to know the truth of Jessica's true family status after Rebecca Randall told her but doesn't try to reveal this.