Well, let me put it this way, these are the skills I would prioritize, and the order in which I would prioritize them for Sera:
Long Shot+
Flask of Lightning+
Flask of Fire+
Full Draw
Looked Like It Hurt (Passive, Subterfuge tree)
Explosive Shot+
This would be the "core" for Sera in my view. Leaping Shot is too risky for AI to use, so I get it later and disable it for AI use (if Sera is in danger just pause and cast leaping shot). At level 11 I believe you should be able to get all of the above skills except Looked Like It Hurt, Explosive Shot upgrade, and one of flask of lightning, flask of fire, and long shot upgrade if you use a respec amulet (they're cheap!). Also if you have any amulets of power, which seem extremely plentiful in the game, you could probably get all of those skills/upgrades sans Looked Like it Hurt.
So if I were you, with just 11 skill points to respec I would do:
Archery Tree:
Long Shot
First Blood
Explosive Shot
Pincushion
Full Draw
Total: 5 Skill Points
Tempest Tree:
Flask of Fire+
Fury of the Storm
Killer's Alchemy
Flask of Lightning
Total: 6 Skill Points
Skills to level up after 11 skill points (i.e. with amulet of power(s) or level up to level 12), in order of priority:
Long Shot Upgrade
Explosive Shot Upgrade
Looked Like It Hurt
Stealth
Long Shot upgrade is really strong against grouped mobs of enemies (which is fairly common if you have the tank aggro correctly). It's a tough decision between taking Long Shot upgrade and Flask of Fire/Lightning upgrade, but ultimately I think the two flask upgrades add a bit more damage than Long Shot's upgrade. That said, if you find any amulets of power... this is no longer a problem.
Explosive Shot upgrade isn't that good, but it only costs you one point and can add damage. It's also one of the few abilities that the AI can't really mess up (unlike say... Leaping Shot).
Looked Like It Hurt is good, but not as important for Sera since she has Flask of Fire. For Varric this is much more important. It's also a 2 stat point investment (Caltrops->Looked Like It Hurt).
Stealth is yet another escape/anti-agro mechanism, and is just a 1 stat point investment. If you find that Sera agros enemies too often and chugs potions and/or dies very easily, then consider taking Stealth above Explosive Shot and Looked Like It Hurt.
Somewhere down the line you probably also want to pick up Death from Above and Leaping Shot from the Archery tree (rolling draw isn't great because the AI doesn't move while shooting T_T), Cheap Shot from the Subterfuge tree, and Ride the Storm from the Tempest tree (requires Flask of Frost and Flaskmaster, both of which are subpar for AI controlled archer).
Also you might consider getting Dance of Death and Sneak Attack passives from the Double Daggers tree. Dance of Death is less useful for Sera than Varric once again because she's less stamina dependent, but it helps sometimes. Sneak Attack is very situational, but any time Sera is hitting an enemy with their back turned (or the back half of their sides) to Sera then she will have 2x critical chance. Neither of these are very useful until like, very late game when you have more skill points than can be usefully spent.
Lastly, don't forget to upgrade gear first and foremost. Rogues of all kinds scale with gear extremely well (DW rogue a bit more than archer rogue because two weapons->two weapon grips+extra masterwork slot). Offensive stats in this game, if you look at the DPS formula, work in a way where stacking offensive stats leads to multiplicative damage scaling, especially with respect to critical chance, critical damage, attack, and flanking damage (for DW rogues, not archers!). If you've ever played say, League of Legends or DotA/Dota 2 it's similar to how auto-attack carries scale into late game extraordinarily well.