why am I not getting the Sleep graphs

Okay so it sounds like her hardware is compatible!

Has she ever got a report showing her the stages of her sleep?

Like this:

Has she read this article?

Track your sleep with Apple Watch - Apple Support

Ok! You and I are posting things at the same time.

It seems like she has NEVER been able to see her sleep stages. I can help you/her with that!

Has she set it up (read article in my last post).

Have her check here:

From the paired iPhone, open the Health app. Click Browse in the lower right corner of the screen. Scroll to and click on Sleep. Scroll down to Full Schedule & Options then click it. Is there more than 4 hours difference between the bed time and wake up time? Scroll down a little ways and look for "Track Time in Bed with iPhone". This toggle MUST be green.

Then open the Watch app on the paired iPhone. Scroll down to "Sleep" and click on it. On the next page, there is a toggle for "Track Sleep with Apple Watch" this toggle MUST be green.

If those things all check out, have here delete the current Sleep Schedule and re-enter it with the exact same times that it had (unless she wants to change the times). Make sure that there are at least 4 hours of sleep time.

Unless I've forgotten a step, tonight it will track her stages of sleep (watch has to have more than 30% charge).

It says that your phone is a 3rd Gen SE. Can you please confirm that? Also, what iOS is it running (Settings, > General, > About)?

What model is the watch and what watchOS is it running (Settings, > General, > About)?

If the watch is running watchOS 9 and the paired iPhone is running iOS 16, then you might be able to get your Sleep data (depending on the capabilities of the watch).

Have you ever been able to get your Sleep data and now it quit working?

Please get back to us with these answers and we can help you further.

Track your sleep with Apple Watch - Apple Support

You said that her watch is running watchOS 9.3.1 and her iPhone is running iOS 16.2.

I'm guessing that the 16.2 is not correct and that her phone is running 16.3.1

She can double check by going to Settings, > General, > About on the iPhone