I don't think she needs a full rework. just some touching up on:
Needs to list increases.
Range increase needs to be increased.
Needs to be cancelled with recast. Possibly multiple targets and cast functioning like Garuda's altars.
For reference, recasting on an altar cancels it.
Augment should be changed to restore energy the same way health is restored.
This ability needs no rework. It can be built different ways, each one valid.
Augment should give shields for all remaining pulses when the target dies, instead of just one.
recast to refresh, like Chroma's Vex Armor, to refresh it without losing the resistance.
Some more duration would be nice.
There is a window upon recast where we are vulnerable, which needs to be removed.
Trinity is a versatile tank, support or even damage dealer.
Outside the points mentioned in the touch-up section, Trinity is not really squishy if built right. Adaptation, link, and maxed strength blessing turn Trinity into one of the best tanks in the game, particularly since she can have infinite energy even with a high duration build.
Her healing and supportive capabilities are well-known.
Build for negative duration and high strength to shred targets for TRUE damage based off a percentage of their health. How many frames do we know of that do %HP true damage? I know of Trinity and Hydroid. I don't know if Garuda's pounce does true damage or not, I know it is %HP though. A Trinity with a decent Rhino roar and sufficient strength can kill enemies at any level with one cast of EV.
Repair is a little bit too powerful right now.
100% HP restored per 5 seconds, or per 2.5 seconds with two equipped, to all allied warframes in 20 meters
Other forms of healing have specific limitations to them or require specific modding and careful management.
case-specific immunity to healing:
nullier bubbles in some fringe cases.
parasitic/energy leech eximii
multiple abilities to cast
Oberon also provides status immunity
Trinity, this has been covered.
Gara has to keep her abilities up after getting them cast on each target.
cost per target
this includes oberon, and hydroid with augment.
Blessing is by far the most potent, able to heal 100% health and shields, but after a cast time, and provides up to 75% reduction for a time.
Hydroid heals a lesser percentage, 30% per 1.5s
Gara's augment is laughable unless considering EHP, at 3 hp/second. also, splinter storm up to 90% damage reduction.
Oberon heals a modest flat amount up front and per second. 125, then 40 per second.
Garuda heals a sizable percentage of Missing Health per second, 25% at base.
Nidus, 20 hp/s at base, slightly more due to strength per level bonus.
khora's Venari, 50 hp/s base.
mend: up to full health and shields
sancti magistar, funny heal based off damage, with a lot of exceptions.
protective dash: 60% over 5s. 5s immunity. applies to everything.
harrow's penance: however much damage he personally deals.
Blessing (Trinity) and Penance (Harrow) are affinity range, which are better. Other abilities are not.
Oberon requires teammates to be in range when he casts, not completely sure on whether it pulses after.
Hydroid's augment requires you to be standing on his somewhat small pool
Nidus, same as hydroid but with a slightly larger static area instead of a movable one.
Garuda's altars, which are medium radius
Gara's splinter storm is cast directly on targets.
khora's venari has to be near allies, and has a short radius
It can automatically move to heal low health allies, or be set to stay near a target.
it teleports if sufficiently distant.
sancti magistar: melee.
protective dash: void dash range, effectively.
Harrow charging shields for penance
Nidus builds mutation stacks to cast his 4
Equinox requires enemies to be killed in Mend's range
Gara has to apply each splinter storm to a specific target first.
Specific conditions to apply healing
Harrow has to damage enemies to heal allies.
Gara has to keep up splinter storm on targets for them to be healed, with the augment equipped.
Garuda has to engage a target in melee range.
Khora's Venari needs to be alive and not be bugged due to pet AI.
sancti magistar: hit stuff.
protective dash: hit allies with dash.
Most healing abilities target every ally except defense objectives.
Venari is an exception to this.
Protective Dash also is an exception.
Repair has very little trade-off involved.
only requires you to be in void form with it equipped, in range of warframes you wish to heal. So you aren't doing damage.
it does only restores health.
Operator survivability, which most operator arcanes contribute to, is not an issue in void form, and you can spend a great deal of time in it. Infinite, with energy restores.
Warframe survivability is also a non-issue. Elevate is RNG and dependent on latency. Nourish is objectively inferior.
Repair only heals warframes, umbra and duality.
TL;DR: Repair is objectively superior to everything we have, SPECIFICALLY regarding uptime on nominal health per time restoration on warframes.
Also TL;DR: I am a cat, and I will hit you with a fish because I feel like it. (How do I fix my profile picture?)