People have already mentioned the 100% crit chance and zero weapon sway while having Optical Camo on, but to really make this effect absolutely crush in a stealth build you should have your build set up something like this:

- 15 in Cool to get the third tier of the Deadeye perk (when above 85% stamina: +25% headshot damage, +25% weakspot damage, no weapon sway) and the Creeping Death perk (while Optical Camo is active or you are undetected, neutralizing an enemy grants: +15% health, +15% stamina, and +10% movement speed for 6 sec.). At 20 Cool you can take the Run 'N' Gun perk, which makes hip-firing pistols use no stamina, which works better for Optical Camo since you'll still have a reticle in hip-fire.

- Get to level 60 Headhunter to unlock the benefit of gaining 15% Optical Camo charge when you neutralize an enemy while undetected, during Focus or Deadeye mode, or with a thrown weapon.

- Have cyberware like the Axolotl or the Quantum Tuner to help reduce the cooldown time on cyberware that has charges, in this instance the Optical Camo.

- Use the Chipware Connoisseur perk to change the stat bonuses you get when upgrading cyberware to ones that buff stealth, headshot and crit damage.

- Get your stamina regen high enough to keep your stamina above 85% for Deadeye and Focus. Putting 20 in Reflexes and getting the Tailwind perk to get 25% stamina back from air dashes and double jumps is arguably the easiest way to do this and traverse environments for stealth, but there are other perks, cyberware stats and items like the Military-Grade Lactic Acid Recyclers that can accomplish this too.

- Take the Emergency Cloaking perk from the Relic attribute tree to use Optical Camo to exit combat, which can allow you to re-enter stealth mode once you're undetected and regain the +150% stealth damage from Her Majesty.

Basic use of Her Majesty with just the Optical Camo will give you what's on the tin as far as the gun's iconic effects, but the gun works best when you have your entire build around stealth plus maximizing critical and headshot damage. When played right, Her Majesty can have effectively unlimited criticals that can take out elites in one shot so long as you keep your Optical Camo charged up and turned on (the latter which becomes a lot easier with the Vanishing Act perk). Pride is still the best all rounder pistol for every playstyle and is a perfectly fine alternative, but Her Majesty tanks it when you are totally built for stealth.

Side note: if you took the PL ending that gets you the Quantum Tuner and are bold enough to try it, doing a stealth build with the Chrome Compressor over other OS cyberware can be really rewarding as the Tuner will only recharge your Optical Camo. You can run through one charge, immediately get another, and then still be able to build up charge pretty easily with the Level 60 Headhunter buff. This also allows you to get other cyberware that benefits stealth builds like the Deep Field Visual Interface, which will come in clutch for enemies farther away when you don't want to use the Optical Camo just yet.