The college assigned us to be a spymistress answering to Van Hal - that's what we should get good at. The mundane intelligence skill .set is highly desirable in a Grey Wizard - even should they reassign us it's as likely to be more spy work as a pure magic role
Mathilde is a journeyman, not a magister. Her job is to learn magic. The college should have assigned her here as a learning experience (officially). If they wanted someone whose focus is to do the actual job, that's what a Magister is for. I think this is the magical equivilent of a year in industry in an engineering course. You're not really there to work. You're there to learn how industry works so you can apply it to your studies..
If they reassign her, they should and probably will reassign her to a pure magic role, simply to keep her development on track and keep her honest. And that way another Grey Wizard journeyman can get the practical experience she's been benefiting from when they substitute them in. You don't want Grey Wizards too used to having power, after all. It's why they take vows of obedience and poverty. I steal from the wiki, who stole it from Realms of Sorcery, but if this applies here:
The only non-Collegiate authority the Grey Order is theoretically answerable to is the Emperor himself, but in effect this is not as clear cut as it would seem. The Shadowmancers serve in war as is their duty as stipulated in the Articles of Imperial Magic. However, Volans, the first Patriarch, and the subsequent Lord Magisters of the Grey Order (led currently by Magister Patriarch Reiner Starke), forbade that the Grey Order should ever sell their skills to aid the various political manoeuvrings of the Elector Counts and other governing bodies. Their goal was to oppose Chaos in all its forms, not to unduly influence the internal political struggles of the Empire. An Emperor could be forced to abdicate, or worse, may fall to the seductions of Chaos and would then stop being an ally and become a potential enemy to the Empire. It was deemed unwise to let the full truth of the Order's abilities and activities get into the hands of a potential enemy; so the Emperor, the Electors, the religious authorities, the Merchants' Guilds, and burgomeisters of the Empire know little or nothing of the clandestine activities undertaken by the Shadowmancers right beneath their noses.
But the Shadowmancers' work is never done. There are many powerful people within the great organisations of the Empire who are Chaos cultists themselves with considerable resources to hamper and block the Shadowmancers' otherwise secret activities. This is partly why the Order is so diffused around the Empire — the more centralised they are, the easier it is to restrict them and follow their movements.
Shadowmancers can be found in service of important officials, merchants, and nobles, whether these groups realise it or not. The Lords of the Grey Order assure all Magisters of their Order are bound very tightly by the Articles of Magic and by the Order's own very strict rules. Shadowmancers may only practice their spellcraft for the benefit of Imperial society and are expressly forbidden from using their magic for their own profit or solely for the political or financial profit of their patrons. All Shadowmancers must take vows of poverty and are not permitted to accumulate property or wealth not of direct and practical use to their cause. Any breaches of the many strict rules laid down by the Order are prosecuted very harshly and vigorously.
After what Mathilde has got up to as Spymistress of Stirland, I suspect that some time back in the Grey College contemplating the mysteries of Ulgu is likely to be on the cards.
Now, she may have some freedom as a Journeyman, but as soon as she becomes a Magister, her actions may become a lot more tightly proscribed. There are a few times when Mathilde has taken sides in internal political conflict between Van Hal and his vassals, for example. And, before it's suggested, I doubt that the Grey College would allow Mathilde to stay a journeyman as a loophole.