This girl I know thinks that I like her sister but I don't really know her?

i've talked to this girl many times as she is a server at a place i go to often. but things have got weird the last while as for some reason she became convinced i liked her sister.

i don't really know her sister at all , i did go to the restaurant she works at ( she is a server too ) its a chain restaurant which is nearby the other one. but we didn't talk and she wasn't my server , i did notice her she's blondish and doesn't look the same as the other girl but there both attractive in the sense

we used to get along really well but the last week or so its been really weird

This girl I know thinks that I like her sister but I don't really know her?
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