I can't emphasize enough how great Nicola's apartment is. Highly recommend staying at her place.
The apartment was extra clean, well decorated, and full of amenities that make you feel at home. It was fully equipped with many extras, including whisky samples, a must. The apartment is located between Edinburgh Castle and the Holyrood Palace, right in the middle of the royal mile. The area is full of cafes, restaurants and some supermarkets, so you can walk to any place you want, you don't need to take a taxi or bus to get anywhere. It is two blocks away from Waverley Train station, which makes it pretty convenient for traveling around Scotland. It is also very easy to get from/to the airport via bus, tram, or taxi.
Nicola is a super host, she was super friendly and fast to reply to messages. She did everything in her hand to make us feel at home. Plenty of recommendations included a good detailed map of how to get from the airport.
Extremely recommended place.