Hey there Katrina-2000,
We understand you're seeing a horizontal line on screen when it the screen is touched. We'll be happy to help.
To begin, check your settings to see if there are any accessibility options enabled that could be causing this. You can view the accessibility settings by going to: Settings > Accessibility
You can temporarily turn off anything that is enabled to see if that helps. For full details on the accessibility features, check this out: Get started with accessibility features on iPad
If the issue persists, our next step would be to restore as new. This will let us know if the issue is hardware or software.
First, back up your data: How to back up your iPhone, iPad, and iPod touch
Then restore the device and set it up as new (without restoring the backup): Restore your iPhone, iPad, or iPod to factory settings
If the issue does not happen, then it is software related. If it does happen, we know service is necessary.
You can restore your backup after testing: Restore your iPhone, iPad, or iPod touch from a backup
If you still experience issues with it set up as new, reach out to Apple Support for next steps or have it inspected. Reference the two links below.
Get Support
Find Locations
Cheers!