She has an older sister but i've never meet her or even knew she existed?

i've been friends with this girl for some time now , anyways she mentioned the other day she had to go to a college graduation ceremony in another city for her sisters graduation as it was delayed by covid and that she actually graduated a couple years ago

but never heard of this sister , i've seen her instagram and is no pictures of her what so ever , but wasn't any pictures of her family which i though was weird

we've also hung out all the time at this pub where she works and never seen her there either , never mentioned her once. her last name is fairly common so perhaps i've heard about her before and didn't realise they were related but can't picture who this person is

i'm not sure if her sister still lives in this area? its possible she left after graduating , it seems odd is no pictures of them together
She has an older sister but i've never meet her or even knew she existed?
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