What law says the owner has to be named on UD?

A non-owner cannot pursue eviction.

You will need to file an answer using the courts form, and in the space provided for other affirmative defenses, put: "the plaintiff is not authorized to prosecute this action"

How would the owner not be in agreement with her evicting tenants? If he knows and disagrees, he would tell her to stop. The owner must be named as the plaintiff in any UD suit; an authorized representative of the owner, who probably does not have to be licensed [e.g., situation of child of elderly owner signing the 3 day notice]. Only the property owner has any legal title to the property so must be the plaintiff. The UD can be signed by a representative of the owner, such as their attorney.