MacBook Pro: Admin account greyed out, cannot reset password

I have my late wife's MacBook Pro running Mojave (could be updated to Monterey). I don't know the login password to her account. But, and here's the thing, I have an admin account on this machine which I can log into. So, I should be able to reset her password (she also has an admin account) from my account, right? BUT when I look at Users & Groups, her account is greyed out, I can't select it to modify. Why is this happening? Is there anything I can do make it possible for me to modify her account? I set my admin account up originally just in case I needed to work on the computer, I've never used it for my own purposes. Now I need it, and it doesn't work! What's the problem? I do have other resources, including the iPhone and Watch associated with that machine, and I know the passcodes for them.