The method of deducting zakaat from a loan

My maid had to return me a loan of 70 thousand rupees. I made up my mind to give her 30 thousand from my zakat money. I had 15000 zakat amount with me, when I gave it to her, she asked how much is it? I said its 30,000 as by that time I totally forgot that it was 15,000 and not 30 thousand. She returned it to me without counting and said that deduct this amount 30k from your loan. Later I remembered the mistake.

Question: is 15k discharged as zakat, or 30k? Should I deduct 15k from the loan amount or 30k?