Wow, this thread has exploded in size overnight. I'll get to the vote later, for now I just want to comment on one thing...
Actually, can she just take the EIC?
Like seriously, what stops her from just saying "Mine"?
The laws of Stirland.
Desire to keep living.
Laws that she could just change?
No.
Now, I'm not the QM, so don't take this as straight canon, and I'm generalizing over a large swathe of history so there are degrees and exceptions, but still...
...a neat thing about a (stereotypical, European history) feudal society is that nobody can really change the laws on their own initiative beyond minor tweaks, things forced by circumstances, and creating new rules in grey areas. People like Suleiman the Lawgiver and Magnus the Lawmender got their reputation mostly on
standardizing a patchwork of existing laws, synthesizing one set of national rules from a dozen sets of provincial and historical and religious rules. There's almost nothing in feudal societies corresponding to a "legislative branch" in the sense that modern government analysis would use the term. Later, historically, would-be absolute monarchs tried to gather all power including legislative to themselves with varying degrees of success, but a feudal monarch isn't really at that stage. A feudal monarch needs to haggle with the towns and nobles just to get armies or impose a tax, let alone confiscate property, and the Warhammer Empire is even more locally independent than most with the Provinces being a loose federation rather than strict subjects of the Emperor.
Adding in the elective thing tends to make the rulers even weaker on this score. A straightforward hereditary monarch at least has a good reason to claim absolutism on the grounds of "My parent owned this country, and I inherited that ownership". An elected monarch tends more towards being seen as a
manager - here to oversee that things run well, ensure the traditions are upheld (and Stirland is
very traditionalist), make those adjustments that are necessary to avoid trouble - but not legislate to create new trouble.
There's an anecdote from the historical HRE where the historical Emperor went to a butcher and kept paying on credit, the butcher eventually said "enough credit, settle your debt now" the emperor said "who do you think you are", the butcher said "I think I'm the guy you owe money to", and seized the emperor and locked him in the meat locker until a servant came from the palace to settle the debt.
This is, of course, practically unthinkable to do in any modern-style society, monarchical or democratic. Modern societies are very, very big on the Weight of Law and Government as abstracted, impersonal, pseudo-sacred things to be carried out only by 'priests' of the Order of Police. Feudal societies tend to run much more on personal claims, duties and allegiances.
So in CK2 terms, Roswita would have to send her Chancellor to forge a claim on the title of EIC. And her Chancellor just quit.
