Yeah, I ask the important questions. ^^ Trixie's helmet has some kind of energy horn thing, which is only active when she's in flight. What does it do? It doesn't seem to serve any aerodynamic purpose, nor does it seem to be a weapon. (There is a moment where Trixie rams headfirst into Rainbow Dash; if the horn is a weapon that would have been a great place to use it, but she doesn't). IT IS A GALACTIC MYSTERY

I will accept "because it looks cool" as an answer

5242059
Maybe it's the suit's version of headlights? Y'know, so she can see where she's going in the dark,

... Yeah, nevermind; even I think that sounds dumb,