First of all, how would the VO find out she lied? We sometimes think these people know more than they actually do.
Still though, I would rather not lie, but that's just me. When I applied for my F1 (10 years ago), my sister was already living in the US, infact she was a citizen, having been born here. My mum didn't want me to mention her bla bla bla. I did, I got the visa. My 2 siblings after me also got theirs, even after my mum had filed a I-130 (family based application) for them.
It really all depends. How strong is her application? What kind of school is she coming to here? Is she receiving funding?