No, a daughter-in-law cannot be a qualifying child. Daughter-in-law is not among the relationships listed in the relationship test for qualifying child, and a daughter-in-law is not a daughter. But a daughter-in-law can be a qualifying relative. See IRS Publication 501 or Publication 17. Or 26 US Code subsection 152.
The link you point to conflates the two kinds of dependents, so do not conclude when it says "dependent" it means "qualifying child dependent."
If you are trying to claim a daughter-in-law as a dependent, it can only be as a qualifying relative. You will see daughter-in-law listed among those that can be claimed as a qualifying relative even if not living with you.
