Hello leslieltran,
Even if you are using Family Sharing, you should not be sharing contacts. That would happen only if you were also sharing an Apple ID. If that is the case, this is expected behavior and there is not a way to separate them into yours and hers. We'd advise that one of you make a new Apple ID for use to keep your information apart.
This page explains further about Family Sharing and Apple IDs: Make sure that each family member has a unique Apple ID - Apple Support.
This article explains how to create a new Apple ID: How to create a new Apple ID - Apple Support
We hope this helps. Let us know if we can assist with anything else at all. Take care.