The easy way to unveil this Riven is to use a stealth Warframe to avoid detection, e.g. Loki or Ivara.

Personally I prefer using Loki as he is able to move around much faster and can sprint and bulletjump while remaining cloaked; this allows me to finish the mission much faster than with other stealth warframes. With the Hushed Invisibility mod I can even equip my favorite sniper rifle and pick off guards at a safe distance without alarming the other guards with weapon noise.

If you prefer to play Ivara I recommend you equip the Infiltrate augment mod as this will allow you to move slightly faster and also allow you to walk through laser barriers without being detected. Also make sure to equip a silent weapon like a bow to avoid alarming the guards.

In both cases, make sure to mod your Warframe for max Duration and Efficiency and also consider using the Flow or Primed Flow mod in order to remain cloaked for as long as possible before you have to use Energy Restore's.

Oxomoco in The Void is recommended for this mission, as there are no alarms in The Void 😉

Don't try to rush the mission - pay attention to nearby enemies, don't take risks but kill them from a safe distance while cloaked. Make sure to pay attention to your remaining energy; if it gets low then find a safe place, uncloak and drop an Energy Restore, wait for it to fully restore your energy bar and then cloak again and continue. Good luck Tenno!