Female betta flaring at a Congo Tetra?

They ARE faster than her, so she can't really catch them to do much damage, but she'll get in their faces and just flare. That's it. Just stare and flare. The Congos stare back for a few seconds before darting away. It's so weird. She doesn't do this to the neons in the tank, OR to the flame gouramis (they both completely ignore each other). So...what is going on here beside aggression? (If anything?)