Sabra decides the largest of the gnolls will best be dealt with after the other is, and she sidesteps to bring her sword into the back of the third gnoll who attacked Jonas.
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If I'm picturing this right, I'm close enough to Jonas and the two gnolls I should be able to five foot step and flank Gnoll 3. (If not, she won't leave the big gnoll if that provokes an AOO, so assume she hits him instead in that case).
Attack: (1d20+3)[9] (Add 2 if flanking)
Damage: (1d10+4)[6]
Edit: Not that I think it'll be enough, but also add the 1 to A&D from the Bardsong.