Fraud Notice 3176C

I really would appreciate some guidance on this, a new situation for me.  The son of one of my largest clients brought me a fraud notice 3176C on his 2017 tax return.  I have talked to the IRS Examiner and gotten a little more time to do an amended return.  He originally filed a joint return with his girlfriend and they claimed ridiculous amounts on the Sch A for medical ($37000) and employee business exp. ($26000).  He made 25,000 on a W-2, girlfriend claimed $17000 auto expense on a Sch C with income of $15,000.  They have no documentation to back it up.  Sticky point is they are no longer together and he wants to amend his return as single and leave her hanging out to dry.  Should we do that or would it be better to file the 1040X the same as the original (joint) or switch and only report his correct income. These are kids and they paid a preparer to do the return who did not even sign the return, but marked it "self-prepared".  Really need some guidance on how some of you would handle this.  Thanks in advance.