How will choosing not to have children affect a woman's career?

Not having children as part of their life could leave them open to opportunities that they might not have been interested in if they had to pick between family or career. 

It gives her the time and flexibility to take on work with a more demanding schedule. You can't travel for work or be on-call 24/7 if you can't leave the kids home alone.

The highest-paying jobs require a lot more than 40 hours/week.

Much of the wage gap between white men and women in America (race adds more factors) is because mothers tend to work part-time or prioritize flexible work schedules over salary, so that they can do all the domestic labor too. Fathers prioritize salary over having time at home, and even over their own health and safety. Therefore fathers tend to have higher-paying jobs than single people, who have higher-paying jobs than mothers.

On the other hand, in regions with a very conservative culture people may look down on a woman who "behaves like a man." Being too obvious about her choice to never have children may hurt a woman's relationships with her boss and co-workers, which lessens her chances of promotion.

It will help you get ahead as you will be able to put in long hours like men do and not have to take months off while pregnant.