Mercy's place is located about 20 mins away from the city center, which makes it a perfect shelter from a busy day in the center. It's in a quiet neighborhood. The house can be little difficult to find, so keep in mind the address and the room number (then it should be easy). Mercy is very approachable, and the room is wonderfully cozy. She's willing to help you with anything (travel tips, the food, room temperature). Also, note that there are cute pets in her house. She has a fine Harry Potter collection too, so any Harry Potter fans should be delighted to chat with her!
Overall, it was a very pleasant stay, and I'd definitely come back to Mercy's place if I visit Edinburgh again.