sedna's heals are OP, u can easily out heal a 3 dps combo(a 3 dps combo fails hard when they have no kills under their belt).
this is how i do it:
to start off i get blood soaked wand, 1 tp scroll, and a health potion
then lvl heal, inner grace, healing wind, and magnificent presence
pounce lvl 1 for interrupt, only lvl 1(its a healing build)
other helpful tips:
never heal yourself in big fights, only use potions on yourself in big fights, you do not want to waste your cooldown or mana.
always use blood soaked wand cooldown instead of using up mana.
always carry health potions and TP scrolls.
anyways, burst damage is very bad with lower cost items, only high cost damage items are useful, mageslayer/ashkandor etc..
the only other useful items imo to counter this healing + shielding is gauntlets of despair or warlords punisher.
other than that, it just comes down to your skills at interrupting.