Problem using the Moto G7 Play without activation Wi-Fi only

It is possible more or less, but by Terms and Conditions you'd receive somewhat frequent notifications to activate the phone, as you described above. 

The problem is not just the constant pop-ups, the bigger problem is that if she accidentally clicks on it, it disables the Wi-Fi and she can't use the phone anymore. How can we prevent that?

So, it's not possible to use the phone without activating it and using Wi-Fi only?

Hi there, ArchStanton. Thanks for contacting us. 

By purchasing a Boost Mobile handset, you agree to activate the handset on a current Boost Mobile plan. To start using your handset with our Boost service, you must agree to the Terms & Conditions on the handset. Can I help you activate your handset today with a plan that fits your needs?

Our terms and conditions require activation on a plan.  If you do not activate, you will not be able to use your handset until you activate it on a Boost Mobile Plan. Data services (including WiFi) will be restricted and you will only be able to complete calls to Customer Care or 911, until you activate your handset.  

We understand. We remain at your service. If you have any other questions just let us know.