I highly recommend Ana's place for a solo female traveler in Mexico City. Ana and her boyfriend (and their cat) are wonderful and extremely nice people: they are always available to help and make you feel at home. I really got along well with them and felt very safe.
Ana's apartment is clean, nice, and located in a great area. The bedroom is impeccable and the apartment's bathroom is for the guest (Ana and her boyfriend have a bathroom in their room), so that is also very nice and gives a lot of privacy. I had a wonderful stay!