I would not recommend a child's bag, the selection is usually limited. If it meets your weight criteria, a little extra room is nice. However, the primary reason is the lightweight bags are usually smaller in width, and are more confining. At 4'11 that will give you a little more wiggle room. Also, the extra space in the foot of the bag is good to stow your clothes for the next day; it will keep them dry and warm. With a synthetic bag you can also dry damp clothes inside the bag with you.

My daughter is also 4'11, and that is a good thing. The world couldn't handle her if she was much bigger!