It can make sense in my opinion.
This chembaroness could have people under her, but at the same time have the mindset of "if a job is truly important to be done, better do it yourself".
Look at Camille, she is the head of her house in the background, too. But she still gets her hands dirty and operates herself, she is effective and uses it for the benefit of her house.
A chembaroness could be the same. They have the sources to make themselves a really effective fighter/assassin. Might as well make full use of it.
Additionally, personalities are different. Not every chembaron has to want to be the mastermind in the background. Maybe she is a crazy chick loving the thrill of an assassination and she doesn't want to miss that just because her influence in Zaun increased heavily.
Another point to consider: Just because the champion plays as an assassin in the game does not mean that they do alot of active assassination in the lore. Chembarons most likely have quite some weapons at hand. Take the one Camille killed in her comic for example. He most likely didn't get his hands dirty, but he still had these lasers to protect himself.
Maybe this chembaroness has alot of chemtech augmentations which would enable her to kill every target at will, even if she does not oftenly make use of it actively in the lore.
There are ways to make it work in the lore, that's all I am saying.
Chemtech assassin would be fine, but I would especially like to finally get a chembaroness.
They are highly influencial beings in Zaun, yet no one is on the level to be a champiion?
We got several champions hunting down the chembarons, like:
It would be nice to finally have a chembaron interacting with them in the actual game and not just reading about them in the lore.
Urgot rework was initially supposed to give us a chembaron, but they changed him to the leader of a cult and he hunts chembarons instead. It makes sense for his lore, I support this decision, but it still leaves us with that lack of a chembaron.