Upgrading from Windows 7 to Windows 10 - don't have user's Microsoft portal password

That doesn't include Windows Licencing.
https://www.microsoft.com/en-us/microsoft-365/business#compareProductsRegion

Thanks for your reply, Edmond... but Microsoft 365 does include Windows 10.  Note that I'm not talking about OFFICE 365. but MICROSOFT 365.

Deploy Windows 10 with Microsoft 365

https://docs.microsoft.com/en-us/windows/deployment/deploy-m365

If you have subscription based Windows workstation, office subscription, you do not need to or are required to use the specific user account.
You can use admin, the user will then login into the Windows workstation using the Microsoft login ......

Thanks, Arnold... clarification, please:  When you say "If you have a subscription based workstation," are you asking if the Windows login is tied to a Microsoft account?  In this case, it is not.  It is a "local" Windows account.  Does that negate our ability to do this?

However, even if the user DID have a Microsoft subscription account based Windows login, and we logged in as "admin" wouldn't that attempt to pull a license that had been allocated to our admin account, rather than her own account?

Two questions. The licensing of the system is based on subscription, that means the user with access to the subscription (administrative) is usually needed.
The license provided is likely KMS that periodically checks whether it is still authorized by connecting to the MS servers and validating.
While I am aware of the subscription based options, have not had a chance to work with those individuals which are likely newer entrants into a business where they do not want or have the capital to buy the software outright.

The license key/product ID is obtained only through the microsoft 365 interface whether it is an individual or a company account....... you need the product Id and potentially the media to install ......

i.e. have dealt with individuals who have office 365 subscription. i.e. the user is entitled to install office365 on 5 devices. But an administrator is not limited to the 5  deployments.
There is an administrative tool that can be used to download the distribution package and roll it out to the systems on the network through software distribution, etc. the activation/access is then granted to the user when they use their o365 credentials in the application.