I had a great stay here and would highly recommend Carmen's place! If you can, spring for this larger room; the other room they rent is much much smaller.
I stayed in Carmen's large room for 8 weeks while on a Huntington fellowship and couldn't have been happier with my choice. The room is large, with desk and tv sitting area, and has a private bathroom. Everything was new and stylish except for the mattress, which seemed a bit old and is more firm than I'm used to. This room is also sunny. The kitchenette is functional but not for heavy cooking. The fridge is also quite small.
The only minor issue is that the upstairs is all run on one thermostat. This room, which has southern exposure on two of four walls, runs much hotter than the hallway where the thermostat lives. Even worse, the smaller Airbnb room has no sunlight and runs even colder than the hallway. I eventually learned to keep my heat vent closed and sometimes open my window at night as guests in the other room frequently turned the thermostat to 70-80 degrees (making my room hotter than 80 because of the sunlight).
Carmen and her co-hosts were very quick to respond to every issue, no matter how trivial. They leave the guests to themselves and, as far as I know, never entered the upstairs premises. I only met one of the co-hosts.
The location is in walking distance to Vons, Walgreens, a very nice laundromat, and is about a 30-min walk to the Huntington. It's on the east side of Pasadena, so not walkable to Old Town.
Guests should be aware that the upstairs is all for Airbnb guest use but is closer quarters than I anticipated. The kitchenette is immediately outside of the two guest rooms, which share a wall. Fortunately, almost everyone who stayed in the other guest room during my stay was quiet, friendly, and courteous, but this was not always the case. While the room itself and the hosts are excellent, you never know what you're going to get in the other guest room. For this reason, the hosts have a camera in the kitchenette for safety, but some may feel uncomfortable being filmed.
Overall, I had a wonderful stay at Carmen's and would definitely stay here again in the future!