I'm guessing that Lebwen successfully downed the L28 goblin. So Silna will wait for the goblin to fall, then step forward and shoot.
Move: to K29/L29, so as to keep her allies out of the way of her shot.
Standard Action: Crossbow attack against O23 goblin unless that goblin is covered from her vantage point; if so, then she'll go with the U19 goblin. Both look within her 80 ft. crossbow range.
Attack - (1d20+6)[15]
Damage - (1d8+2)[3]
Spoiler: On a threat
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Crit Confirm - (1d20+6)[26]
Crit Damage - (1d8+2)[9] Actually, I'm not sure if Favored Enemy bonus damage gets multiplied or not...