Thanks for asking this question! Like others have shared, larger companies have started publishing diversity reports which can show you how many women they have in different departments/ different leadership roles, etc.
I encourage you to look for companies and teams with female leaders - having a role model that you can look up to and imagine yourself in their shoes is a great way to feel like you can succeed in your job. Another good opportunity is joining an employee resource group, here at New Relic we have a group called "Women @ New Relic" that is a great way to form community, learn and grow.
The AnitaBorg Institute (AnitaB.org) runs the annual Grace Hopper Celebration of women in computing, which is an incredible conference to attend - they have scholarships for students that you can apply for. The exposure to brands and businesses through talks and their career fair can help you find a company that you're interested in applying for.
The most important thing, in my mind, is to find a company whose values align to equity - look for examples of their C-Suite execs talking about diversity, equity and inclusion and decide if it feels like the kind of company you want to work at and could thrive at. Not every company is a good fit for everyone, so rather than just looking for where you can get promoted fastest, I would look at where you will feel fulfilled, given opportunities to grow and be in a space where equity is a mandate.
Finally, community groups outside of your company are a great way to also figure out ways to get promoted or move forward in your career. Here in Portland Oregon, we have a group called PDX Women in Tech - there are similar groups (or Women Who Code) in cities around the world - and being a part of these organizations is a great way to learn about which companies are supporting women, and to meet mentors, sponsors and role models!