In the beginning you can only rely on brute force to even get to higher tier skills. Since every other Demigod seems to think of Sedna as an easy kill, I ususally have a very slow start staying back out of sight and trying to pick off things even easier like unsupported grunts an the odd flag capture. I would like a bit more movement speed with Sedna from the beginning to do at least that effectively.
I tend to get the Swift Anklet as a favor item on bigger maps. Later on I'll get the Boots of Speed (always get Monk Idol with my first 1k gold). Throw in Inner Grace and I zoom around the map. You are right that early Sedna is best at hit and run, but always remember to stick with your teammates. A solo Sedna can be effective though no where near as effective as she is in a group. Remember that Pounce is an interupt so even if you aren't throwing out heals from the beginning you are still helping immensly with your interupt. And your Monk minions will keep you healed enough to keep you on the battlefield. Just don't get caught in a 2v1 or higher conflict. Sedna can't handle being out numbered in the early game.
Nowadays I don't bother even getting the single heals because I run out of mana too fast casting them and they are too slow in casting to effectively save someone "from the brink of death". I still think there is a valid strategy in teaming up with Rook for example. But you would need a teammate who plays along and possibly voice com to pull it off. It doesn't work with randoms.
Well now that is just crazy talk 
Heals are vital for yourself and your teammates. Plenor's Battlecrown and Velmish Hat(?) gives you plenty of mana and they are relatively cheap. I run Pounce, Silence and then enter the "healing stage" while I melee where I am ready to heal myself or teammates as needed. Once the enemy DG starts to flee or hits low enough health I finish with another Pounce.
Pounce and Silence are possibly great once u get there. I find it very difficult to use them though in a fight. You have to learn the animations of the skills of the other demigods by hard, you have to get the timing right (the other demigods have fast skills too) and you have to do that on top of constantly moving out of harms way yourself and issuing commands to your rather dumb minions, who tend to fall asleep every three seconds. Especially those Yetis annoy me. The minions could use quite a bigger aggro range. This is all quite micro intensive.
I agree it takes some timing practice to be effective with Silence. Even after playing Sedna for so long I still end up casting Silence and interrupting nothing because the enemy was just doing melee. Still when it works it is worth it.
That is most of my gripes with Sedna right now. In a couple of long games I managed to get her to 20 or near there and the combination of aoe-healing buff, tier IV minions, Yetis and some of the other minion buffs was very powerful. At the moment that is what I go for mostly.
Minion builds are rough early and even mid game, but once you have your army powered up you can really tear it up late game. That being said, I never touch the Yeti line. I tried build after build after build in beta trying to convince myself that a minion build would work and just never could. You lose so much of Sedna's utility by spending skill points on Yeti and Morale.
I think I will try Oak next and see if he better fits my playstyle. Shame for Sedna though, I really liked that character. If that doesn't work out, I will revert to Rook and admit that I am too old to play micro intensive games
If you do, keep an eye out for Ralsar. Oak and Rook are my favorite minions, I'll keep you healed 
