In Snow Falls we see the funeral of King Leapold where Snow is saying her final good byes to her father and hugging the queen. At this point the kingdom is still loyal to Snow White. The queen knows that the kings gaurds would not harm Snow because they are all giving their condolences. The queens mirror is the one who suggests the huntsman. We know that the queen said that “she” refuting to Snow White couldn’t keep a secret.
This is what caused the queen to be angry at Snow White. If we watch Heart of A Lonely Hunter we see that Snow White knows that she has angered the queen and knows that the queen wants her dead. With the princess out of the picture the queen becomes the next in line to rule the trown and can do what she sees fit with anyone in the palace; dispose of them and call upon her own men.