Tell you daughter not to worry. His threats to counterclaim against her are nothing more than that. It’s spurious. He’s grasping at straws.
In the first place he would have the burden of proving by a preponderance of the evidence that there was an express agreement between the two in which she agreed to pay for his labor.
Secondly, even though such an agreement would not need to be in writing (provided that the work could be completed within one year) he is going to have a tough time explaining away why his so-called labor claim suddenly first surfaces years down the road after the romance cooled and is now being sued on his promissory note.
If he can’t come up with convincing evidence that (1) she agreed to pay the $15K before the work was started, nor (2) produce documentary evidence showing his account receivable and (3) proof that he consistently billed her for the labor long before she started her lawsuit, the judge will toss his counterclaim back in his face.
Besides, the dollar limit to recover a debt in Ohio small claims is $3K. So if he expects to have his claim for $15K litigated, the entire proceeding will need to be removed to a higher state court and it is doubtful that he is going to come up with the money to hire an attorney to proceed in that court. He sure as heck won’t know how.
Just make sure that she has the necessary documents to prove her case in small claims. He ain’t going to show up anyway!