The reason he stayed so alive in her head is because of oof her fascination with his stories that she remembered perfectly.
Explanation:
Even if uncle Marcos had not visited Clara for a while, she would always picture him by closing her eyes. Clara remembered her uncle very well, he was the only vivid memory from her childhood.
When her uncle would visit he would spend his time going after Clara.
Through those stories, she became very connected with her uncle, so it can be said that those stories kept alive the memory of her uncle.
