Response : After you lose a challenge in which Sarella Sand participated as an attacker, kneel 1 influence to choose and stand 1 participating character.

I apologize for the dumb question, but is this ability limited to once per challenge, or can I use it as many times as I can supply the influence? An example of what I'm talking about would be I attack with Sarella and two other characters and lose. If I have three 1 influence locations, can I stand all three attackers?

(2.4) Responses Per Trigger
If a response or passive ability is triggered,
the effect can only occur once per trigger. For
example, if Sansa Stark (CORE S9) is in play
and you play an attachment on her, Sansa
Stark's effect (draw a card) can only be triggered
once. (If a second attachment is played
on Sansa Stark, her ability can be triggered
again.)

So no, you can't keep kneeling influence and standing characters because her ability is a Response and you only lost one challenge. It's the same reason you can't use Robb Stark (Core Set) to kill every one of your opponent's characters after winning just one military challenge.

Thanks ktom. I didn't think it would work, but I couldn't remember why.