How to set up medication reminders on Apple Watch S9 for my daughter

Is the watch completely updated? Medication reminders only came to the watch with watchOS 9

Please see this on how to set up medication reminders

1. Open the Health app on your iPhone or iPad.
2. Do one of the following:

• • On iPhone: Tap Browse, then tap Medications.
  • On iPad: Tap the sidebar, then tap Medications.

1. Tap Add Medication (to start your list) or Add a Medication (to add to your list).
2. To identify the medication, do one of the following:

• Type the name: Tap the search field, enter the name, then tap Add.
  • In the U.S. only, suggestions appear as you begin typing. You can select a suggestion, or finish typing the name, then tap Add.
• Use the camera: (U.S. only; on iPhone SE (2nd generation and later), iPhone XS, iPhone XR, and later) Tap  next to the search field, then follow the onscreen instructions.
  • If a match isn’t found, tap Search by Name, then type the name (as described above).

1. Follow the onscreen instructions to choose the type and strength of the medication. If you want, you can also create a custom visual of the medication and set a schedule.
2. When you’re finished, tap Done.

See this link for further reference

Track your medications on Apple Watch - Apple Support

If it is not working this is due to your iPhone controlling her watch, it might be that she needs an iPhone of her own to set this up.

You can try and do it on your iPhone, but when you’re seeing in the instructions that i send, is that you’ll need an iPhone to set the reminders up unfortunately