It is impossible to delete the App Store app. It is on the iPad somewhere.
Search for it using Spotlight. Swipe down from the middle of any home screen. Type in App Store at the top. When the app appears it will list the folder name to the right of the app icon if it is hidden in a folder.
If you are using Screen Time and parental controls, you may have disable the App Store which will hide it.
Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
Finally, you can reset the home screen layout to return it to the home screen, but that also destroyed any app structure that she may have on the home screen. Settings>General>Reset>Reset home screen layout.