Activation lock

She hasn't completely removed the phone from her account. See the 'If the previous owner isn't with you' section of the article below.

Turn off Activation Lock - Apple Support.      

You bought your phone second hand from someone other than Apple or an authorized Apple reseller. Unfortunately the phone will be useless to you. The links below explain what has happened. You didn't know to heed the advice given below.

Before you buy an iPhone, iPad, or iPod touch from someone other than Apple or an authorized Apple reseller, make sure that the device is erased and no longer linked to the previous owner’s account. 

And see: Activation Lock for iPhone, iPad, and iPod touch https://support.apple.com/en-us/HT201365 See

this heading Check for Activation Lock before you buy a device from someone else.

What all this means to you is that there is no way we can help you. We are not authorized to remove the activation lock from any phone. And, under your circumstances, Apple will not help you since you cannot provide proof of ownership that Apple will consider to be sufficient. All I can suggest is that you try to recovery the needed password or your purchase price from the seller.

Your receipt for the purchase of the device from Apple or an Apple authorized reseller with its serial number on it is what you need.

Did you try another WiFi connection? If you have a WiFi connection, I am beginning to wonder if she has really done the steps in the article.

Troubleshooting Wi-Fi issues in IOS.    

Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch         

Try a forced restart.

Reset Device.      

Didn't Apple Support try to deal with that problem? What happened assuming they tried?