Ans 1:
Class : Class 10
"By her own" is incorrect in English because the expression is generally "on one's own." We use "on her own" to convey that she did something independently.
"Quite some" is a grammatically correct expression that emphasizes the quantity or difficulty of the books. It means that the number or level of difficulty of the books is surprising or impressive.
Corrected Sentence:
"My daughter's friend has read quite some difficult books on her own."