The Contingency Plan

my older sister called me today. she's actually my half sister but oh well.
i found out about her when i was eleven. the dinner table was scattered with homework and drawings and mum and dad sat down together facing me and simply said i have an older sister who's coming to live with us soon. she was from mum's first marriage (when mum was 18) and when mum got divorced, chinese law stated all children were their father's custody. mum has missed her a lot. they've fought for years to regain custody.
i was ecstatic and made plans of what we could do together.
a few weeks later, my very affectionate family was shocked by an angry and rebellious teenager that wanted nothing to do with us. the following years were extremely rocky and rebecca left home when she was 18. she was married by the time she was 21 and at the age of 30, has three sons with her very strict italian husband. she doesn't even spend money without asking him first. he's head of the house and she respects that.
i see her perhaps once or twice a year. she called as she found out i'm pregnant. i felt bad as i forgot to tell her. she honestly slipped my mind, perhaps because she plays such a small part of my life now.
we have very little in common, we share different values. she still finds it hard to accept my relationship with lucas because we're together and not married. she's not flexible, i have no desire to be close to her and feel terribly guilty for it.