Short version: Study salaries in your area, your employer (glassdoor.com) and evaluate your skillset as objectively as possible. Then negotiate as though your employer does not discriminate and try to get a fair salary. If they attempt to offer you too little, negotiate for more. If they refuse to pay you a competitive wage, regardless of their motivations, then find another employer who will. Software Engineering is a field in which there is a labor shortage, you have the power to shop for an employer who will treat you fairly.
Long version: You seem worried about the wage gap, but don't worry, it almost certainly won't affect you. To explain why, let me give you some background.
In the United States, the statistic commonly known as the "Wage Gap" comes from the Bureau of Labor Statistics Highlights of Women's Earnings report which they publish annually (I have linked the 2013 report.)
First, a quote from the first page:
It is important to note that the comparisons of earnings in this report are on a broad level and do not control for many factors that can be significant in explaining earnings differences.
The report looks at a sample of all earnings in the nation and does not attempt to compare men and women in similar fields with similar experience.
Due to the fact that the Bureau of Labor Statistics report was being used in a misleading way to warn of a "Wage Gap", the Bureau of Labor Statistics contracted with the CONSAD Research Corporation in 2009 to do a more thorough study that would control for factors like experience, career interruptions, and industry. It can be found here.
A few quotes from the foreword:
During the past three decades, women have made notable gains in the workplace and in pay equity [...] However, despite these gains the raw wage gap continues to be used in misleading ways to advance public policy agendas without fully explaining the reasons behind the gap. The purpose of this report is to identify the reasons that explain the wage gap in order to more fully inform policymakers and the public.
Although additional research in this area is clearly needed, this study leads to the unambiguous conclusion that the differences in the compensation of men and women are the result of a multitude of factors and that the raw wage gap should not be used as the basis to justify corrective action. Indeed, there may be nothing to correct. The differences in raw wages may be almost entirely the result of the individual choices being made by both male and female workers.
As some commenters have mentioned above, recent studies have shown that for unmarried men and women early in their careers (before things like career interruptions due to pregnancy generally come into play) and in the same field, the earnings gap between men and women is very narrow, with some reports even indicating that women earn more.
Pew Data for 2012, showing women under 35 making 93% as much as men.
Guardian article from 2015 reporting women in their 20s earning more than men.
Anecdotally, I also currently work as a Senior Software Engineer myself, and have not observed gender to be a factor in salaries among my coworkers, and have never heard a manager bring it up in salary discussions.
The only real danger is not negotiating effectively (this cost me a lot of money early in my career, even as a man.) I recommend the book Getting to Yes as a good starting place if you have never taken the time to hone your negotiating skillset.
So in summary, don't let the Earnings Gap discourage you. Learn what people earn in your market, know your skillset, and negotiate confidently and assertively for what you know you're worth. The data shows that employer discrimination is not a significant cause of the Earnings Gap, and as I mentioned earlier, if they do try to discriminate against you, the best choice is to walk away from the table and find another employer.
Best of luck!