To make sure your assistant correctly addresses your contacts, share them with her. This way you can also choose how she’s supposed to handle your calls and make a distinction between private and professional calls.
When you download the iReachm app, you’ll be asked to give acces to your contacts. Click OK to do so. If you missed this step, don’t worry, you can still share your contacts afterwards. Therefore, go to your Settings of your mobile phone. There, you’ll have a list of all your apps. Search for the iReachm app, and activate the option Allow iReachm access to “Contacts“.