Two gamertags in one MS account?

Thanks again. I will impose on you one more time. Can you tell me how to edit the existing gamertag and remind me how I assigned her a gamertag in the first place? Please understand that I was a network engineer for more than 30 years and solved problems that would cross Solomon's eyes, but this is way outside my wheelhouse. I'm sure I can eventually figure out how to do this, but a little guidance up front will save me a lot of time.

Yeah. I know. I was being sarcastic. I have discovered how to edit my gamertag. That was easy. I have created a gmail account for granddaughter and then created a Microsoft account for he. She is now in our family group. So far it has been easy. However, I have hit a snag trying to get into her hypothetical (at present, anyway) Xbox profile. The "How to create . . .) popup has links for Windows 10, Xbox, Android, and iPhone. The Kindle is an Android device, so I select that, and it provides a QR code and instructs to scan it with the "Android phone" and then log in to her MS account. I will cross my fingers and have a go at that.

https://support.xbox.com/en-US/help/account-profile/profile/change-xbox-live-gamertag

Microsoft accounts and Xbox accounts are essentially the same thing so it may have had a gamertag assigned to it when you created your account and you may have just changed it at that time or she's using one that was randomly generated. Or you were prompted to add one when you signed into an Xbox service.

Thanks. What is this "Xbox" of which you speak?

Microsoft's gaming services