As others have said it's always best to go to the source and ask your aunt. If you are talking about real estate if it is listed for sale in NYC that information is available to agents on REBNY & the MLS and other websites as well. If it is a private estate sale through an attorney it may not be listed but sold directly to contacts of the attorney or through a RE brokerage. as an "exclusive " or pocket" or in- house listing. After the sale is recorded you can find that info via a search of the NYC property Records. If you are concerned because of an interest you may want to contact a local estate attorney..(If it an estate sale as in objects you could contact the local auctioneers or check craig's list.) Ok?
I assume you mean selling the house, not the contents. I agree that talking with her is the most direct way to find out. Are you interested in purchasing it? Are you asking because you want an opportunity to buy it before she lists it? If, so probably best to chat with her. In the alternative, if you want to see if it is already listed, I would check the public real estate websites like Trulia and Zillow. I don't know if there is public access to the local MLS in your area, but if there is, that's the best way.