Let me point out the obvious first: it sounds like you are a teen. You are each struggling with the normal challenges of
1) negotiating changes to your social life
2) navigating the world of dating and
3) trying to figure out who you are becoming.
It’s natural to be somewhat different around different groups of people. We all do it. You probably behave differently around the guys compared to when you’re with her, if you’re honest with yourself. For example, you’re probably louder, your language is coarser, and you’re probably more physical with your male friends (e.g., playful shoving and pushing).
It’s also natural to “try on” different sides of oneself as a teen tries to figure out exactly where they fit on a femininity (or masculinity) spectrum. The truth is that perhaps she is BOTH of what you have witnessed; perhaps she enjoys being a “girly girl” sometimes, especially around certain friends, but also enjoys the sincere, sensitive, one-on-one conversation with you. Cut her some slack. Realize that you do it too. Take a risk and ask her out.