How can I stop my daughter from turning off her location?

See the following from Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Allow changes to privacy settings

The privacy settings on your device give you control over which apps have access to information stored on your device or the hardware features. For example, you can allow a social-networking app to request access to use the camera, which allows you to take and upload pictures.

To allow changes to privacy settings:

1. Go to Settings and tap Screen Time.
2. Tap Content & Privacy Restrictions. If asked, enter your passcode.
3. Tap Privacy, then choose the settings that you want to restrict.

Here are the things you can restrict:

• Location Services: Lock the settings to allow apps and websites to use location
• ...
• Share My Location: Lock the settings for location sharing in Messages and Find My Friends
• ...

In order to stop a child from turning off their location, do we need to be on that child's phone in order to lock it? I have been in screentime and family sharing on my phone and do not see an option to stop a child from turning off their location. As you can see below it says my child is not sharing her location. I would like her ability to turn that off blocked.

And then what? Once you have the phone with you what steps are next?

You will need to be in possession of your daughter's phone to make the parental control changes that you wish to enable. In most cases, it will not take more than a few minutes to do this if you know what you want to change.