Screen Time not working as expected on daughter's iPhone

Depends on how you have it set up.

• Are you the Organizer on a family plan?
• Are you setting the limits on your device from the Family or only on her device?
• Are you using a Passcode for Screen Time that she does not know?
• Are you setting the limits by Category or Specific Apps?
• Is it a specific app you are having trouble with?

Set up Screen Time on iPhone - Apple Support

Some common ways kids use to workaround the limits is by signing out of their account. This can be prevented by going to Screen Time > Content & Privacy Restrictions > Account Changes, and set that to Don't Allow.

Another thing they many try is changing the time zone on their phone to mess with the time. This can also be prevented by first going to Settings > General > Date & Time on her device, and make sure "Set Automatically" is turned on. Then back in Screen Time you can lock the setting by going to Screen Time > Content & Privacy Restrictions > Location Services > System Services > Setting Time Zone, and turn that off. Then tap the Back button and on top of the screen choose "Don't Allow Changes". Back all the way out and it should no longer allow her to change the Time Zone.

For TikTok specifically, I would suggest to use that Apps Parental Controls as it it much more comprehensive then not only restricting Screen Time. In addition to the Screen Time, you can restrict who the child can communicate with and also the content they can view in their feeds which currently may be inappropriate.

TikTok Parental Controls

The heavy handed approach for a child looking to bypass the settings is to remove the App, then prevent them from downloading it again by going to Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Installing Apps.

For platforms that also have access to their content by viewing a web page without needing an app, you can block access to that website. In the section here called Prevent Web Content, there is a section where you can block access to a specific website.

Use parental controls on your child's iPhone or iPad - Apple Support

Make sure all devices are updated to the latest software they support. Where loopholes have been found, Apple has included the fixes in Software Updates. Even with everything set correctly on the device, there are other workarounds such as using Zoom to call a friend and the friend can allow them to control their screen to use any app on their device.

For a child determined to defy your wishes, there are still flip phones that cost very little and it is amazing how cooperative they become with the thought of showing up to school with a flip phone.