Well, remember her dad died when she was young. Sometimes, these things just don't come up. Her mother may not have been close with the dad's fraternity brothers and they really didn't have any seemingly obvious reason to play a major role in her life after his passing.
PS SigDelt<3, would you happen to be a member of Sigma Delta Tau?
[asking even though it may seem like an obvious one because a few weeks ago, we had LoveSigDelts and I was like, "yay! maybe she's a sister!" and then she wasn't...]