We had a great stay at Julieta's appartment. Julieta is a very welcoming person who makes you feel comfortable and she's willing to provide you with any information that you need.
The appartment is pretty, decorated with good taste in a traditional Mexican style. There is a supermarket about 10 mins away walking, and Julieta doesn't mind you cooking.
Coyoacan's center is about 15 mins away by foot.
Finally the appartment is located in a safe and quiet area, the only thing that may disturb your night is what seems to be a machine that the gas station next door turns on at any time of the day or night (the noise isn't that terrible though).
Julieta's appartment is definiely a fine option for anyone who'd like to stay in Coyoacan's area.