They need to file a police report, and get in touch with their bank. It's likely the money has already been transferred to a different bank, but the corresponding bank might still be able to freeze the account if it is still sitting there.
Then again, it might be transferred again as well. Money is hard to trace if it moves through different jurisdictions, as every country has different banking and privacy laws. Your client might very well hit a dead end for such a (in the grand scheme of things) small amount of money.
Highly unlikely - but also, a side fact to keep it from happening again. The attack similar to this I had to help address, someone had sent an email to a client, over an Indian shared office space network. That network was found compromised, and man-in-the-middled. Suggest doing business communications like email over VPN (F-secure VPN or simlar) only.
Then again, it might be transferred again as well. Money is hard to trace if it moves through different jurisdictions, as every country has different banking and privacy laws. Your client might very well hit a dead end for such a (in the grand scheme of things) small amount of money.