At season 2 episode 6 ("Changing") Kara is training with Mon-El. At one moment she is in the air and waving at someone. Was she waving at the people who control the wires to lower her down or is it something else?
It does look a lot like she's waving to someone off-camera, possibly the person controlling her flight harness. That would be a bit odd, though, since the shot's clearly not finished, as there's dialogue still going on. So, while it doesn't really look like it, I think it probably was intended to be in character.
She begins waving in response to Mon-El reminding her about being drunk the previous night. As she drops to the ground, she continues waving her hand vaguely at Mon-El, in the universal gesture for "please stop talking about that", and then asks him never to bring it up again.
My guess is, she was actually just turning her head away from Mon-El and trying to wave off his comment, but because of the camera angle being below her (as opposed to at eye level), the whole gesture just looked strange.