[What has been the most difficult for Ni to adjust to in the Mass Effect universe?]
((There are probably quite a few things she's had to make an effort to adjust to... different technology, humans being a significantly more prominent race, the other races all being different [especially the presence of the asari and absence of the vazoral, since the two bear a passing resemblance (although there are male vazoral), and the latter is a species composed almost exclusively of militaristic, bigoted slave-drivers... yeah XD], her not being able to visit Earth anymore, her not having her usual contacts (she spends large quantities of time outside of easy contact distance from anyone she knows, but she still likes to know she could go and visit if she needed to), but... I think her biggest adaptation is also the most obvious one: The Mass Effect Universe is going through a much darker time right now than the Future 101 universe.
Oh, there are malicious forces that could potentially pose a threat to the entire Milky Way, and perhaps even the immediately surrounding galaxies if they REALLY put their mind to it, but right now they're all currently in a state of either "biding their time" or focusing on the small, sure bets in terms of conquest, rather than going on an all-out attack (the fact that there's more than one race that could potentially threaten the entire galaxy is, itself, a reason to consider not threatening the entire galaxy, for fear that one of the other forces in question might object :-p), where as the residents of the ME Universe currently have the reapers to deal with.
On top of this, of course, the version of the ME Universe Ni is currently dealing with has magic-anons plaguing it in the worst possible way, as well. Now, of course, these same entities could start menacing Ni in her own universe, but thus far Ni seems to be being largely ignored by the resident gray-faces, as has the few people that have visited her universe (at least while visiting), so... again, this is presently a difference.
More than the direct influence of these, though (even though knowing Earth is currently infested by ultra-powerful kill-bots does bother her a bit), is the effect they seem to be having on others, as well as just the natural differences in mood the two universes seem to have: The Future 101 Universe seems to be a much more up-beat and, to be honest, all-around silly universe than the Mass Effect Universe, and having to accept that the residents of the ME universe, especially the "important" ones, tend to be a bit darker and edgier is something Ni's having a hard time getting her head around.
It doesn't help that the one Shepard Ni currently has the most familiarity with (which is, admittedly, still not much) is the quintessential renegade and, as such, worse than most space-pirates she's had to contend with in her own universe :-p.))