I missed commenting on your initial submission of chapter one, so I'll start there.
First, the hook line. It's not quite strong enough to hang out on its own. It either needs to get stronger or grow a paragraph. As it stands, it feels like a heavy-handed proclamation of its nature as a hook. I prefer more subtle approaches to hooking the reader.
The next few paragraphs aren't much better. They don't do a good job of getting my interest. I think a big reason why is that Mia doesn't actually do anything for quite some time. All we know is that some girl is sitting in a tree watching a mansion, but not why, so it's not very interesting. If you were to come right out and tell us from the start that she's there to steal something, then we would have a mental framework on which to drape the scene and our interest would deepen. Also, if at all possible, I'd prefer a reduced density of difficult (for me) frenchy-sounding names right off the bat, as each new unpronounceable foreign name adds to my mental overhead.
Note, also, that the scenes with Jannas also doing nothing stack on top of the Mia-doing-nothing scenes and heighten the effect. These are scenes that, were this a movie, would probably occupy around 30 seconds of screen time. They should fly by, but instead they drag.
Once I get over the barriers of the first few sections, though, I had a grand old time with the story. I thought the way you portrayed Mia as a petty thief turned upscale procurement specialist was artfully done, and I liked the way you wove the bargaining with the client in with the narrative of the job. You know, you just know, that the ending will be exactly what it was; but, since it was not at all telegraphed, it's a delight when it arrives.
One major snag was the whole Santa Claus act. I'm not buying it. Now, granted, I've never actually seen the top of a chimney up close, but, at least from the ground, they all seem to have small openings on top. I don't think she'd fit. Also, it ought to have a flue, which would further obstruct her passage upwards.
Then, Mia takes care to clean her boots so as not to leave tracks, but then presses her body against the mansion, which ought to leave a big fat smudge.
On to chapter 2! In this chapter, we're mostly just getting to know the characters. I like all of your characters, and think they are generally skillfully portrayed. I don't have much to say about the chapter specifically, but the following general comments apply to it as as well as chapter 1.
Above all, I'm itching to give this a good copyedit. Since that's completely impossible considering my schedule ATM, I'll have to settle for pointing out the line-edit-level faults in a general way.
Watch out for things that ape the Wheel of Time. Several details, like the nature of common rooms, calling underwear "smallclothes", the pyrotech with an Illianer accent, etc. look to be lifted directly from the Wheel of Time. In the big, important details you're unique enough, but those little things kill.
Dial back the hyperbole a bit. For example, the client dude fainting when Janna brought out the shard was a bit melodramatic. The kid who fell in the fountain from shaking his head was also over the top; would anyone really shake their head *that* hard? There are also several other examples of hyperbole that need to be dialed back, which I should have written down as I read because I can't recall them now.
Watch out for said bookisms. At one point you have someone frowning a sentence, which doesn't make logical sense.
Lastly, watch out for portions that lack finesse. Here's one from chapter 1:
The Magistrate’s jaw dropped, and he struggled for several moments to form words. “That is absurd!” He said, his knuckles turning white as he gripped the edge of the table. “Pay you eighty gold crownes before the job is even accomplished? No, I will not give you a single copper rose until I have the shard back in my hands!”
“Then our discussion is over,” Jannas said, rising to her feet. She brushed out the sleeves of the white blouse, lifting one hand to summon a serving girl to remove the empty cup and saucer. “There will be no arrangement, and the acquisition will not be made. Perhaps you will have good fortune, and Magistrate Renécheric will decide to keep your secret and tighten his hold over you. You must have some final shred of dignity he can remove...”
She looked him in the eye with a flat stare. “Or, you can hand over that bulging purse on your belt and finally have the matter done with.”
Jannas talks too much here. It seems more in keeping with her personality if she were to stop at "Then our discussion is over." Keep staring at him, tap your fingers impatiently. He'll break down.
Also, he balks at 80 crownes but later forks over 100. Simple continuity error?
That's it. Nice work overall on this. I look forward to the next.