The stealth challenges are pretty annoying.
One thing to note is that, unlike the Taskmaster challenges, it's often best to not go after everyone you can in an area, even if it's safe to do so, because sometimes leaving a guy all vulnerable on his lonesome will trigger a Photobomb, which, if he's the last guy left in the area, can be done very easily and net you an extra couple thousand points.
For this challenge, the photobombs don't seem entirely random, so it might just depend on what order you take out the mooks in, and knowing where the photobomb will show up should allow you to get yourself into position. Aiming for the cameras is a bot annoying, but they can be webbed up.
Web strike takedowns makes it so much easier, and web strike doesn't actually break stealth if you manage to get a guy on his lonesome. (I mention this because I spent a long time thinking only perch takedowns were silenced, but it turns out perch takedowns just make it so bodies can't be discovered, which if you're going through the challenge quickly enough, shouldn't be a problem anyway).
Cameras can be webbed to temporarily disable them, though aiming at them is a bit annoying.
I don't think you need ultimate ranking in all the challenges to unlock her sidequest, though.
(The challenges I hated were the combat ones, personally. Damn photobombs seem random, and occasionally needing to run over to one, wait for baddies to come to me, and hope they get to me before the challenge runs out makes the whole thing feel way more luck based than it should be.)
