So Being Sued By Mentally Unwell Person. Are We Really In The Hole On A Lawyer?

Thanks everyone in advance for giving this a read. We are new to the "being sued" game. This person claims defamation out of pure delusions of paranoia. This person is well known around the circle for being borderline (if not completely) schizophrenic. This person sued my SO and some other people, but only my SO has been served.
This is an open and shut case we would like to think, and have plenty of evidence and character witnesses to completely disregard any claims this person has made regarding defamation. Is this something worth representing yourself on or is it actually necessary to pay money for a lawyer/fees/etc just because a person like this has filed a lawsuit? I am aware of counter-suing for court fees and the like, but I doubt this person has any money at all. We're assuming this person got a tax return a few months back and decided to finally go looking for people.
I will try to provide more details if needed but am of course being discreet in this matter. Thanks again.
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