Cristina's apartment is cozy and very bright. It's in a very quiet area, with a big supermarket just around the corner, and few minutes walking from Sintra's main train station. I stayed there for a month and I had everything I needed for a comfortable stay. The view of the Castelo dos mouros and Palacio da Pena is just amazing, especially at night, when they're lit.
Cristina was very nice and helpful, she answered all my messages right away, and the check in and out ran very smoothly.
Just two things to bear in mind is that the flat is on a second floor and there's no lift. It's not a problem but be aware if you're carrying a big suitcase. And the family living upstairs can be a little bit noisy in the morning, but again not a major issue. I would gladly come back and stay again at Cristina's place!
Enjoy your holidays in this very lovely town, it's magical! :)