Overview

While Henrietta might share her firearm with the T-Doll P90, their roles are entirely different in practice. Fortunately, Henrietta's extremely impressive base stats let her perform relatively well as an Evasion tank despite her odd kit. 

The skill description and exact mechanics are worth an entire novel, so let's summarize the two main use cases in terms that are easier to understand. 

Performance as a Main Tank

Henrietta starts every battle with a 10HP shield, gains Evasion over time if her shield is ever broken, and can activate her skill to gain even more shield - with more evasion stacks contributing to a stronger shield. 

As a result, Henrietta performs very well when tanking enemies that deal relatively little damage, due to her passive shield and skill mechanic.

Conversely, she underperforms when enemies are highly accurate or hit for a lot of damage. 

Henrietta's tile buff cannot buff ARs in tile 1 if she's placed at position 5, but she can buff the offtank with Damage and Accuracy thanks to her tiles affecting both ARs and SMGs. 

While Henrietta can't tank as well as dedicated evasion SMGs like C-MS or Dorothy, she's potentially worth training if you're in need of more durable main tank SMGs. 

Should I manually activate Henrietta's skill by waiting for max evasion stacks before triggering her shield? 

This is a difficult question to answer, since if not done perfectly the extra Evasion/effective HP you gain with manual skill will very likely be offset by allowing Henrietta to take more scratch damage. 

In general, auto skill will work fine. Only players confident in their calculations and kiting should try delaying Henrietta's skill activation.

Is it necessary to adjust Henrietta's RoF to gain maximum benefit from her skill? 

In terms of skill timing: no. Henrietta can benefit from the stacks gained at 2s and 4s even if she activates her skill immediately (so if she lost her shield at battle start, she'll gain 2 Evasion stacks by 4s, and her active will provide a 40HP shield).

In terms of her active's RoF-buffing component, Henrietta only needs 2 stacks to cap out her RoF (and even 1 stack brings her extremely close), so there's no point trying to minmax that, especially since her DPS output is fairly poor to start with - see below. 

Performance as an Offtank

While Henrietta can work as an offtank, she offers neither the AoE burst nor strong sustained DPS. 

While Henrietta's skill has a +Damage component, even at max stacks (+30% Damage stacked three times) she cannot come close to dedicated DPS offtanks like SR-3MP (+260% Damage) and cannot buff the backline like Honey Badger (+160% Damage, plus +Damage/Crit tiles for ARs on tiles 1/7).

Even in 2x Main Tank formations, Henrietta is outperformed by JS 9 in both coverage and tanking ability.  Furthermore, Henrietta's tile buff formation requires her to be placed in Tile 2 (and ARs in tiles 1/4) to fully utilize her buffs, which is not ideal, especially since B formation is generally harder to kite to start with. 

• It is therefore not recommended to use Henrietta as an off tank unless you know what you're doing.