I'm on a new replay right now, and still on Act II, so the latest version of the build I'm tinkering with isn't complete yet. When I hit level cap, I'll post the completed version.
For me Battlemaster is absolutely the way to go when it comes to building a solid, all-purpose tank. The Rally/Unite ability, keeps Aveline, and the rest of the party nicely topped up with mana and stamina, as well as letting them share the benefits of Aveline's other defensive talents. I like to have this as a priority cast on the tactics screen, that way I can get away with only putting around 18 points into Willpower for the none-Mage party members, allowing them to really stack up their DPS stats instead.
Fearless Synergy boosts defence for all party members, reduces damage taken, and provides a constant, passive taunt that affects all foes in proximity to the aura, allowing Aveline to round up enemies like iron filings to a magnet and keep them focussed upon her, then we have the remaining talents that keep Aveline's stamina maxed out pretty-much most of the time.
I favour Constitution when assigning stat points, because I don't care about DPS, and can gain sufficient fortitude from other talents, and have two other Sustained abilities active 24/7 - Turn the Blade and Shield Defence, that's a whopping three sustained abilities running constantly, but it doesn't matter, because the Battlemaster talents allow her to quickly recuperate energy. I also grab all passives that reduce/mitigate damage or boost protection.
This generally makes Aveline almost invulnerable to normal attacks. I also use the free DLC belt 'The Irons' to boost elemental resistance. The only things that can really hurt her are damaging AOE attacks, such as the ones generated by Arcane Horrors. She's pretty much useless against the Sky Horror in MotA, but then, that's what I bring other party members along for.