We stayed at Teresa's place for 1 month and can not recommend it. It is cheap and a good location, just 20 minute walk to city center or Alfama. Note it is hilly so make sure that is okay for you.
However, the apartment had many issues. It was tidy but not clean when we arrived. Dust throughout it (the headboard was disgusting) and black mold on the ceiling in the bathroom and bedroom. The apartment was always damp, clothes felt damp,bed felt damp when we went to sleep. Nothing would dry.
Also,appliances broke on us multiple times. The Air con was broken the whole time we were there. Technians came twice but could not fix it. Also, the oven stopped working (we had only used it once before) and when we told Teresa, we didn't hear back from her for two days and that it would be fixed after we left. Very disappointing experience.