My mother was included on unlawful detainer complaint? She moved out years ago at LL request, which he acknowledges.

If a default judgment was entered against your mother, she can file a motion to set aside the default and default judgment, probably on grounds of improper service of process (e.g. if she was never personally served, and was supposedly substitute served at an address which was improper). You would not have legal standing to do this on your mother's behalf unless you are a licensed Cal. attorney.