Hey there Krjohns55,
We see that you are having some difficulties with setting up the voicemail on your daughter's iPhone. We would love to assist you with getting that voicemail set up.
First, let's make sure that we have your cellular data enabled on the iPhone before setting this service up: Check the cellular data usage on your iPhone and iPad
While reading this article, make sure you are specifically following the instructions in the section titled "Turn cellular data on or off".
Then try restarting the iPhone to set up the voicemail: Restart your iPhone
Also, make sure that the iPhone is up-to-date: Update your iPhone, iPad, or iPod touch
Lastly, try resetting the network settings on the device: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
Follow the steps of this resource, in this section titled "Still can’t connect?" for instructions on how to reset the network settings. Be mindful that you will be prompted for the network password again once you complete this reset.
Hope these resources help!
Kind regards.