I had a lot of fun with the healer frames from Firefall, so here's my idea for one, with a bit of a twist
1) Medium frame
2) High mobility, average defense, minimal offense
3) Thinking medium power core, possibly heavy depending on how much the abilities use
4) Scales of Life - This frame isn't a typical healer. Instead of replenishing/repairing health, it transfers damage around between allies and enemies. It does this by moving damage from one unit to another, for example, if a lighter, mobile frame takes a big hit, it would take some health from a beefier, heavy frame or an enemy, and replenish health to the target frame, healing more than it takes. This also allows it to be a tank healer, taking health from the enemy or from an allied frame that isn't taking too much damage. It can also transfer damage from one unit to many, allowing a tank frame to take a massive hit by distributing the damage among the party, and letting other healers take over spot healing
5) Some kind of nanite cannon? or ray gun or something. This is what allows the frame to use it's ability. I think locking the shoulder mount to the Scales of Life also helps balance it out, since it's a pretty powerful ability
6) Heavy Shotgun. This frame is going to be in the thick of things, dancing around and through the fight. It's shotgun has a decent knockback effect, helping it get out of rough spots and helping it maneuver enemies for its allies
7) The Libra: A frame designed to help even the odds between the Gatestriders and the T'si-hu. It can hold its own solo, but the more enemies and allies it has around it, the more powerful it becomes. It's offensive power is minimal, but it's Scales allow it to save it's allies from the brink of death, and bring down judgement upon its enemies.