I have some girls that have pretty pronounced bulges, so I generally sex them by looking for preanal pores. A 10X jeweler's loupe really helps out when you want to sex young specimens. Also, if you are good at "popping", you will have a definite answer. BTW, be sure to have a good light source when using the loupe.
Your specimen looks female, but it is hard to say. How much does "she" weigh?