The bad grammar in the sentence is due to a double negative: "By answering, she could not do no less". A correct way of stating it would be "By answering she could do no less."

Can you link the original Italian?

ok i had a go at this and so did my wife who did an english degree!!! my effort is --------------- By answering, she could not help but look at him. He was a very tall, and rather handsome boy. Compared to her he was far too beautiful. She was powerless to admit her desire for a relationship, however congenial, with him. All she thought of was him. However she did think that he would be more handsome with his hair cut short and without the hair oilhe so often used. As she stared, she tried to imagine just who could he be, what his job was, and ,even if anything in his appearance could suggest it, she imagined that, maybe, he was a engineer. She was inclined to believe that because, among her secret memories, there was one concerning a young engineer, who once lived near her and he was always arguing with his wife. And she, who then was only eleven years old , fell hopelessly in love with him. That was her first great love, the greatest love anyone had known . “I'm sorry, I wasn't paying attention”, she said, realizing that the boy was looking at her with a equiring expression, as if he was waiting for a answer. (...) -------------- my wifes By answering, she could not help looking at him. He was quite a very tall, and rather handsome boy, next to her he was far too beautiful. She was unable to admit at all the possibility to have a relationship with him. What she thought was only for him; how she would prefer he had not a so tidy hairstyle, with that hair oil, like in newspaper advertisements. He would be more handsome with hair cut short and without hair oil. The she tried to imagine who could he be, what his job was if anything in his appearance could suggest it. She believed that, maybe he was a engineer. Howerver she was tempted to believe that just because, among her secret memories there was one concerning a young engineer, that once lived near her and he was always arguing with his wife. And she, that then was only eleven years old and attended primary school, hopelessly fell in love with him. That was her first great love, the greatest love; greater than any the world had known.). “I'm sorry, I wasn't paying attention”, she said, realizing that the boy was looking at her with a inquiring expression, as if he was waiting for a answer. (...) hope this helps

(…) By answering, she could not help but looking at him. He was quite tall, and rather handsome, compared to her he was far too beautiful. She was unable to admit at all the possibility of having a relationship! She thought only of him, and what she wanted. For example: in order to be liked more by girls he kept his hair untidy using oil, like in newspaper advertisements. He would be more handsome with his hair cut short and without hair oil. Then she tried to imagine who he was and see if there was anything in his appearance that could suggest his occupation. She believed that he was an engineer. Among her secret memories she held a memory of a young engineer that once lived near her. He always argued with his wife. She was eleven years old and attended primary school when she first fell hopelessly in love with him. That was her first great love. The greatest love which anyone had known. “I'm sorry, I wasn't paying attention”, she said, realizing that the boy was looking at her with an inquiring expression, as if he was waiting for an answer. (...) There are a lot of run on sentences here and I tried to not chance what you were saying. There still are some errors but I hope this helps.

(…) By answering, she could not help but look at him. He was a tall, and rather handsome boy, compared with her he was far too beautiful. She was unable to comprehend the possibility of having a relationship with him. Her thoughts were only for him, and she wished that he, in order to be liked more by girls, hadn't such a tidy hairstyle, with all that hair oil, like in newspaper advertisements. He would be more handsome with his hair cut short and without hair oil. She tried to imagine who he could be, what his job was, and ,even although nothing in his appearance could suggest it, she believed that, perhaps he was an engineer. She was induced to believe this, because, amongst her secret memories there was one concerning a young engineer, who had lived near her and he was always arguing with his wife. She, was then only eleven years old, fell hopelessly in love with him. That was her first great love, the greatest which anyone had ever known. “I'm sorry, I wasn't paying attention”, she said, realizing that the boy was looking at her with a inquiring expression, as if he was waiting for a answer. (...) Sorry I tweaked it quite a bit. Hope it helps.