If there were a Writer's Bible given so much detail on character intricacies, either nobody wrote it, nobody read it, some writers actually came from another planet and had difficulty converting unit distances to ensure a unified consistency within character traits for the sake of suspension of disbelief or credibility, or a generalized mindset of "The audience won't notice, it's a small plot bypass detail, who cares, just as long as Jellico doesn't tell her to put proper clothes on" even though she did wear a proper Medical Blue uniform early on.
As Takeru also indicated, empathy also involves recognizing facial expressions. By innate intellect or even by rote (which is something many with Asperger's Syndrome can accomplish), or both, the problem with that is that Picard and the rest of the bridge crew will see the same facial expressions, hence the usual audience retort of "She's saying the obvious, Captain."
Granted, ignoring the details - if the story is otherwise good enough - has some terrific payoff as, for example, "Encounter at Farpoint" shows a few great Troi moments as she is the only one who's able to to figure things out because of her ability. The big downer is, not all episodes can be the same way with nonhumanoid or incorporeal life forms, though more of those wouldn't have hurt - at least until the audience recognizes the template and ends up saying "When's Troi going to say the obvious." There's no way to win. She's a great Q-detector, though. She always gives out good Q-tips just before he pops in.
Only in "Nemesis", after how many years or decades, she's finally given a new ability - despite her stating early on she can only read minds, not send thoughts. In that movie, she's sending them the same way burger flippers push out 3-for-a-buck specials. "Buck" as in dollar, raise your hand if you'd eaten venison, in which case "3-for-a-buck" makes even less sense unless you change the context of what "3" represents as it can't reflect burgers, unless the buck's size is so inadequate that only 3 can be made from it and why the heck am I talking about that... oh yeah, it's nigh on lunch time... Morningstar Farms has these fantastic meat-free burger patties made with processed soy and mushroom and beans and other pulverized vegetable bits, which are actually quite tasty, though science now claims soy might be harmful... what a bunch of partypoopers... and what's a hamburger without buns, preferably whole grain and high in fiber...
So anyway, I'd say her range is a couple thousand miles or so, not including other factors like the species she's trying to make a diary out of and how far their abilities to project extend, which - like walkie talkies - makes reception a lot easier and more fun. As she in an episode discussed how she can tune out others' thoughts, in a way Tam Elbron couldn't. Good episode, "Tin Man", odd title though... I think there was another one as well where she mentions tuning out others' thoughts... such a range is impressive for any species with such abilities, for which in real life the number of capable species is "zero", which might be for the best. Lion A thinking "That tasty succulent dinner is over there by the tree and rock and lake, braying ever so loudly" (or however the lion perceives these things to be, I doubt they use English or anything approaching written or verbal linguistics to that distinctive extent) and Lion B is just sitting a hundred yards away writing down notes. The pedantry does lead to some amusement, but where in the biological development does a species - without technological assistance - develop supernatural or esper-like capability to a quantifiable extent that can no longer be written off by the locals as "folklore", "superstition", "what's found in a bag of fertilizer to grow crops big and strong with", et cetera. Much less what other beings might postulate about without knowing both the capable species and its norms.