I didn't realize that was part of the Old Testament canon.
If her husband died, she could hope to be cared for by her adult children
Doesn't sound like a very stringent law to me.
I'm waiting for a chapter and verse on this requirement. Those who keep asserting this "fact" should be prepared to provide some documentation. A vague reference to the Book of Ruth doesn't suffice.
Let's begin with you pointing me to the chapter and verse that supports sola scriptura.