Question

Because being very sick, she couldn't go to class
---> Because of

Answer 1

Because (of) being very sick, she couldn't go to class
---> Because of her sickness, she couldn't go to class.

P/s: Câu ở trên để viết lại sai cấu trúc, phải là because of

Answer 2

Because being very sick, she couldn't go to class.
---> * Because of her sickness, she couldn't go to class.

* Because of the fact that she was very sick, she couldn't go to class.

=> Cấu trúc với because of:

Because of + N, S + V

<=> Because of + V_ing , S + V

<=> Because of the fact that + S + V, clause.