Can a verbal agreement be taken to court?

The only thing she can do is wait and see if he really does take it to court and if he does, she will need proof that they lived together and that the heating installation was needed and purchased. She will need the proof (bill of sale) of the amount of the heating installation. She should also keep and bring the threatening letters that he has been sending her, because by rights she could have him charged for threatening her, (as long as there is proof). If he keeps bother her that way she can call the cops and charge him with harrment and put a restraining order on him. He would need some sort of proof if he wants to take her to court for this money.