Before considering court action it would be wise to remember the maxim that 'you can't get blood out of a stone'. If the guy doesn't have the money (or assets which he can convert to cash) your mother could have a hundred court orders and still not be one penny better off. So don't bother going down the route of court action unless you're reasonably confident that there's some chance of getting the money (or at least a part of it) back.
The absence of a specific settlement date, on the document which relates to the loan,
might be regarded as a problem by the courts. However, it's more likely that a court would view the loan as similar to when a bank provides an overdraft. (i.e. the lender has the right to cancel the loan, and demand repayment in full, at any time).
No court would rule in your mother's favour unless she could show that she'd made a formal written approach to the borrower, demanding the return of her money. She should therefore start by sending the guy such a letter, in which she should indicate that she intends to take court action if the money is not repaid to her within, say, 28 days of the date of the letter. Your mother should obviously keep a copy of the letter. It should be sent by recorded delivery (even if the guy lives next door to her) so that she can show the court that the borrower has received, and failed to comply with, a written demand for repayment.
For information about the court procedures, see here:
http://www.hmcourts-service.gov.uk/infoabout/c laims/index.htm
Chris