We are a similar team, so I can share what you do. And my daughter was the only girl on the team when she joined.
We are open to students from anywhere in our county, though we don’t allow students who have their own team at their high school. We have students from several smaller schools, private schools, and our middle college (high school students who attend high school at a CC.) We do a presentation at each school at least once, and we always set up shop during open houses or technology events. There have been several different ways to present at high schools: we have had the robot in during lunch periods for students to check out, we have done formal presentations for freshmen, we have recruited eighth graders in the fall, we have had our shop open during open house to greet students and parents, etc. Each school varies depending on what they are willing to give us.
As far as the girl issue… I was just having a great discussion with my daughter who is home from college. She was the only girl on her team at first, though she recruited others. But it wasn’t always easy. She was told to sweep a lot, she was told to “stand there and look pretty”, she was pushed aside. Luckily, she is a fighter. But not all girls are. There are threads you can read here, but the biggest point is often missed: it’s not as much about the things men do on purpose, it’s more about the things you don’t realize - the “climate.” In general, girls need more freedom to make mistakes without ribbing, more time to feel confident in a task, and more encouragement to try something new (not their fault, they were probably told before that they aren’t good with tools.) My daughter notices on her engineering teams that the girls wait a bit longer to jump in, but then they tend to be more skilled at first once they do. However, if an environment is allowed in which they are pushed aside before they get a chance to absorb a task enough to feel confident jumping in, they never will.
The good news is that encouraging students to pay attention and understand a task before they start it is good for everyone, not just girls (it’s really good for the team budget, too!) And creating an environment where it is safe to fail without ridicule is good for boys as much as girls, too.
There’s a lot of room for improvement in the FRC life of girls (I could tell stories!), and it’s commendable that you want to address that. Just being aware will help, trust me.
Practically, if you can find a girl from another FRC team (or a few) who would be willing to help you at a recruiting event, it might break down the boys-only stereotype created by a bunch of boys showing up. A female mentor for your team would help a lot, too.