I need an answer

[CASIGKAP]

Here's my problem ladies. One of my best friends is an Alpha Phi alum and her sister is attending my school next year. She would be an Alpha Phi legacy. However, she has recently asked me to not mention her to anyone at school nor to tell her sister that she plans to rush b/c she wants to explore the options that we offer. There are 7 GLO's at my school, Alpha Phi being one of them.
I think it's great that she wants to find where she's more comfortable rather than automatically going where her sister went. My dilemma is that I feel terrible lying to my friend who just figures that her little sis is not interested in Greek Life.
What should I do? Keep lying to my friend and keep the confidence or tell her the truth? Neither option sounds too appealing to me but I'm stuck.

What do you think I should do?

Thanks for any advice! You guys here always seem to help me with my problems!