I'm having trouble using her though. I mean, sometimes she just stops following me and she becomes useless. Didn't have that problem with D-Doge
They serve different purposes. Quiet doesn't really follow you like Doge does. Doge is a living soliton radar + active decoy who can also attack but can't take much damage. Quiet on the other hand is more like a mobile sniper turret who needs to be positioned, but can also operate away from you unlike Doge. Very good for flanking over long distances, scouting out bases before you even get there, and being a viable distraction who can draw enemy attention from you without being in close proximity.
Use your iDroid to position Quiet based on how you need her to function.