Yes, this is plausible.
There are many ways to work around the lack of physical prowess of the torturer, with many of those solutions also serving to highlight their skill, or cruelty, and the overall horror of the act.
I'll focus my answer around a particular example, Sand dan Glokta from The First Law series by Joe Abercrombie. Minor spoilers follow. He is one of the main characters of those books, and his primary calling is that of a torturer. What makes him interesting is that he himself is a cripple as result of being captured and tortured by the enemy in the past. His left leg is useless, he is missing half his teeth in a way that the ones above do not line up with the ones below, and he is in constant agony as a result of his scars. He is an absolute terror to look at, which makes his character all the more potent when he shambles out of the dark corner of the room during a torture sequence, and then leans over the victim to smile with his half empty mouth.
His appearance adds to the feeling of powerlessness that the victim is depicted in. Any healthy person would easily be able to over power Glokta if they were freed, but when they are bound, this disparity in physical ability only highlights their own weakness. The backstory also adds a nice touch, since Glokta is never shy about explaining his appearance to his victims. He himself has experienced many of the tortures he inflicts upon his subjects. He knows exactly what it feels like, and he does it anyway. And this is noticed by both the characters and the readers, adding an extra level of mental horror to the actions.
Of course, as a physical cripple he cannot work alone. He uses a number of physically imposing goons to capture and restrain his prey before he begins his work. Your character will need some similar construct to explain how they get past the capture part of the process. Perhaps they are very devious, and lure people into traps. Or use some poison to render their target unable to resist. But once the person is in their control, physical strength matters little in the process.
The character I described above works nicely in the role of a torturer, because he subverts the audience's expectation of what a torturer should be and what they should look like. Your character has the same potential. No one would expect a twenty something woman to whip out the torture implements and know how to use them, yet that is exactly what occurs. Let your character use this expectation in their work. Play up her weakness, implement it into the scene, and just run with it. You want her to be frail and often short of breath after a physical task? Stick a comfy chair in the middle of the torture room for her to retire to for rest, while the poor soul she was working on gets to stare at her from wherever they're restrained.
