Is a cash gift or payment for her services unethical?
Something to consider is that frequently the listing is by the broker not the realtor.
Commissions are sometimes split by the brokers THEN again between the broker and realtor, meaning that instead of the 6-7%, the realtor may only get 1.5% or so if there are splits.
You can do the math and see that she may not want hassles and hard feelings over a thousand dollars or so.