Why was it so important for Renee to hide the fact that she was very intelligent?
Renee explains that the reason she must hide the fact that she is an autodidact and very intelligent is because "It has been written somewhere" and "It has been decreed." She states that since everyone expects her to be old, ugly, fat, have bunions on her feet, eat cabbage, have a cat, watch TV all day, then this is what she will pretend to do. And this is what she does pretend to do. She brews coffee that she never drinks, she buys disgusting food that she feeds to her cat, she turns on the TV all day but she never watches. She is a "permanent traitor to her archetype" she says.
Renee does not pretend around Manuela, however. Manuela is like her, pretending to be something she is not. She is so much more than a mere housekeeper, just like Renee is so much more than a concierge. Also, When Mr. Kakuro arrives on the scene, figures out what Renee is all about and befriends her, she also lets down her guard around him.
So, based on what you know about Renee's childhood (have you read that part yet? If not, you need to read it), you will see that Renee has grown up with an inferiority complex. This can be inferred from the reading. Renee has low self esteem, but loving friendships begin to work on her to raise her to a level where she can be comfortable with who she is. And then she dies.
Read about it here on eNotes.