Lior,

If your friend purchased trip cancellation insurance then they can make a claim against the insurance carrier and get a refund per the policy terms. However, barring private trip cancellation insurance coverage, it is entirely up to the airline whether or not to refund them and how much, at least in the United States.

You should ask your friend to consult with an Israeli legal expert who may find an exception to that general rule under requisite Israeli law. Even if some exception can be found, it is likely not worth pursuing it as the legal costs would far outweigh the value of the funds sought to be recovered.

In my opinion, your friend should write a deferential letter to the customer service manager, attach the doctors note, and ask for a voucher in the amount of the ticket value to be used on a future EL AL flight.