At level 10, I loaded up with potions and regeneration flasks: if you're not a mage - make sure you take two mages instead of one. I took Cassandra as my tank, and set the AI so that everyone's preferred tactics were Guard/ Barrier/ Cold /WarCry/LifeWard abilities and spells. I then took over Cassandra while my main rouge just went crazy with poisoned arrows.
Both mages went berserk with cold spells and barriers - and I put Cassandra to work on the dragon's hind legs. We didn't retreat, and for the most part until the dragonlings were in my face, I ignored them.
It took a while, but they bought down the dragon with only 1 death (who actually revived before the end).
Last note: if either of your mage takes and damage early, before they fall under the regen potion threshold, have them quaff a regeneration potion. Save the full heal potions until clutch time if you can.