If a pregnant women is HIV positive and she is treated with medicines to deliver a normal child,can she transfer the HIV virus back to her normal HIV free child by colostrum?
Yes, it is possible and the chances are pretty high. According to the WHO paper linked below, the rate of partially or completely breastfed children which get infected by this route is about 20-35%, while the rate of children which are not infected and doesn't get breatfed is zero (no surprise here).
The mechanism by which this infection occurs is currently unknown, but it is hypothesized that the virus enters via the mucosa. See these two articles below for more information: