She should put the sealer she wanted to on the hearth. It will seal in the cat smell

She didn't smell it until she tried to clean the hearth so it can't be that strong.

Ask if she has tried Natures Miracle. It has worked for me where my cats "missed" the cat box and instead dribbled/sprayed urine onto a tile floor. NM is a liquid enzyme cleaner found in pets stores. As I said, it works for me and my cats.

She went to Petsmart and found something called (I think ) Stink free... and she said that worked pretty well and now is applying the first coat of sealer. She said she can't smell any more pee. Thank you for your responses.

Spray the brick with plain white vinegar. It might take a couple of applications, but it WILL work. Over 30 years ago we bought a home with a crawlspace. Everytime it rained, the house stank of cat urine. We ripped out the carpets thinking they were the source. Found out from neighbors that the previous , elderly owners allowed their cats to use the crawlspace as a litter box. We did one good douse of white vinegar and never smelled it again in the 17 years we lived there.!!!