My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
If you are using an Iphone there are a couple of adapters it looks like for this model here to make your Iphone work with your system.If the adapter cables were not installed this needs done and I can help to let you know which one you need depending on the Iphone being used.There was also an issue with a software update for the Andriod system on phones that use Android.Let me know which phone you are using and we can continue from here.
If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.
Is this connector being used at all for her Iphone?http://www.crutchfield.com/p_130CDIU52/Pioneer-CD-IU52.html.If not this needs obtained so the Iphone 6s works with this system.If it is let me know.
Have you checked to see if there is an option to turn off the mute feature.I know some of the Pioneer models had this feature and it had to be disabled in the settings.Let me know.
An audio install facility should be able to unmute the phone issue here.I know I have seen some issues with mute on or device not recognized on some Pioneer models using an Ipod connection so most likely you are running into the same issue here.
Try to reset the phone while it is plugged into the radio by turning it off then back on and see if this works.If this does not then an auto accessory/audio installed should know a procedure for this model here to correct this issue.
Let me know if you need anything else and feel free to rate my help.