OK, I get these two possible totals:
InMe is In 8 + Me 6 + Int 4 + MT 6 + MT specialization 1 + Inventive Genius 3 + Aura 5 + Lab General Quality (includes familiar) 8 + Items Specialization 8 + Me Specialization 1 = 50
InCo is In 8 + Co 7 + Int 4 + MT 6 + MT specialization 1 + Inventive Genius 3 + Aura 5 + Lab General Quality (includes familiar) 8 + Items Specialization 8 = 50
So 50 either way, plus probably a couple of points more from shape and material bonuses. I don't see any applicable ones in either the main rules or The Mysteries, but you'd think there'd be something involving detection.
The range would pretty much have to be Voice (Sight requires a separate InIm effect, in addition to another magnitude), and the duration Sun, so that's 3 magnitudes, plus another 4 points for continuous effect. Ergo, she could easily manage something with a base effect level of 5 with a lesser enchanted device, and probably a base level of 10 by involving Chryse. But the device wouldn't have a way to contact Viola, which would force an invested device, or require someone to carry it around..
And I'm not sure how many devices we'd need, but the Amazons have shown themselves able to travel off the roads, which makes the problem rather intractable. If we've got to make multiples of this, invested devices just aren't workable: that's an enormous amount of time and vis. I'm not sure even multiple lesser enchanted devices would work, even if I could think of a feasible one. And even without the problem of meddling fae, I'm not sure we do any better with the Animae Magic devices.
Getting someone to carry a device around might work better on both fronts (no need for additional enchantments, and mobile enough to cover multiple routes), but if we can send out scouts, why do we need the magic items in the first place?
One thing that does occur to Viola is that the creek fae would be friendly enough to be persuaded to keep an eye out, without any need for magic items--that's short-range, but still potentially useful. Also, would recruiting birds or other wide-ranging animals as scouts be an option?