Guest post by "Z" I agree, that's apprehensive. He doesn't look horrified at being in public like this, just very nervous about what's to come.
This is something some activists do that isn't okay. Forcing people to make a statement that they aren't comfortable making. It's especially bad in cases like this, where you're trying to make the point that everyone should be allowed to present as they're most comfortable... by forcing someone into a presentation they aren't comfortable with! Having a comfort zone and boundaries is okay- it doesn't mean you don't "support the cause". I'm complaining about adults who do this- Marta's a kid, I don't see it on the same level. I do think she was wrong to do this, though.
I'll bet what's really going on is that Marta is actually very nervous about this, and having her brother doing the same and supporting her is giving her the strength to keep going with it. I imagine she didn't ask in part out of fear that he'd say no. It wouldn't surprise me if she's not consciously aware of this, if it is the case, a lot of people act without truly realizing their real motivations.
