Sister's original work is one eighth of Siu Wah Yuk's original work1/4 *1/2 =1/8.

Now my sister's book is equivalent to Siu Wah Yuk's original 1/4+ 1/8=3/8.

Now Xiaohua's book is 1- 1/4=3/4.

Now my sister's book is a fraction of Siu Wah Yuk's, 3/8÷3/4= 1/2.

Or you can think so.

Xiaohua divided her books into eight copies on average and gave two copies to her sister, twice as many as her original books, and her sister had 1 copy.

Xiaohua has 8-2=6 copies.

Sister has 1+2=3 copies.

So 3÷6= half.

Now my sister's books are half those of Siu Wah Yuk's.