That’s true to an extent. But you have to remember Brigid isn’t technically the same part of the family, she’s extended family – though very close extended family.
Brigid feels like she has to work extra hard and make up for not actually being Ryan and Valera’s child and sometimes feels a little ‘on the outside’, like she doesn’t truly belong there. So she wants to do everything she can to fit in and make herself less of a burden on the people who have chosen to look after her. Of course that’s not true and Ryan and Valera love her like their own child but it’s hard for Brigid to fully understand and believe that.
Whereas Elizabeth feels like she’s the most important child of the family. She’s the oldest of the Fontaine kids so feels like she deserves all these things and shouldn’t really have to work for it. A lot of that is jealousy of Brigid though – she can clearly see how much Ryan and Valera, and the whole family, love Brigid and she has this voice in the back of her head that says everyone loves Brigid more than her. To her, that’s not fair because Brigid isn’t even part of their family – she’s not her sister, she’s her cousin.
They’re both still just teens though and people grow and change a lot through their teenage-young adult lives so don’t worry, things won’t stay the same forever. Elizabeth certainly has a lot of growing up to do especially. They just have to experience a bit of life and grow as people and find themselves first, then things are sure to change!