Her kit is somewhat conflicting.
Her passive gives her attack speed after every spell, similar to Lee Sin. But she eats all her spells in one combo.
Her E draws in all units towards her but she is squishy and most viable as a single target assassin.
Diana has the kit of being a capable fighter, but she isn't viable as one. I contend that she should have a bonus hp ratio on her shield and her E should give resistances based on each champion pulled (similar to pre-change Xin ult).
Consider lowering the base damage on her spells and increase their respective ratios to compensate (tentative suggestion).
This would encourage Diana to be built as a more tanky/bruiser type mage who could duel and engage large teamfights. She would still be able to build burst in mid but can now option fighter in jungle and top. Think of that cancer tank ekko meta and remove everything that made him cancer.
> no % health damage
> no permaslow
> no roadrunner utility MS steroids
> no 'press R to restart' ult
Her CC has a high cooldown.
Her defenses and shield reward initiation and are punished if you choose not to.
No real escape if you choose to initiate.
Final and perhaps most important point from a design perspective is that Diana now fullfills a unique role. No longer is she just another burst mage. She now becomes a durable fighter with a lee-sin esque, long range initiation pressure within teamfights - only her job isn't singling out targets it is grouping them together for the team.