This is completely unlike any magic in Tanya's previous world! In fact she'll just go ahead and conservatively assume she fundamentally doesn't understand how magic operates here.
As far as Tanya knows, magic is the result of the application of a mage's will, limited by that mage's mana. Few people are born as mages and nobody knows why, or what mana is or how magic operates on the level of physics.
The direct use of magic has been practiced since prehistory and is borderline useless. The easiest way for a mage to boil a kettle of tea is to chop wood and carry water. The mages of ages past laboriously built elaborate apparatuses and complex chemical processes that could convert a spark of magic into something precise and repeatable... but they never significantly affected either technology or society.
Until the invention of the modern computation orb. In just a few decades, applied magic went from the equivalent of abacuses to general-purpose programmable computers. Vast swaths of modern industry rely on mages as vital work force, to say nothing of the military, and they compete desperately to hire them. The Germanian Empire, the world's indisputable leader in computation orb technology, has even gone so far as to conscript sufficiently capable mages, giving its army and vital industries first right of refusal on their labour.
That was the happy world Tanya Degurechaff was reborn into, precious human capital that could rise in society even after being orphaned and abandoned as an infant... So of course some idiots with no understanding of basic game theory blew up a minor border conflict into a world war that has already ruined three major nations and is on track to destroy all the rest in the next few years. (Good riddance to the commie bastards, pity about the rest.)
What magic in Tanya's world decidedly did not do was appear somewhere all by itself.
It would take several hundred skilled mages with modern equipment to produce a total output of magic comparable to this forest, assuming they had a (completely ridiculous) spell that would produce such a complex and well-synchronized flow. Of course, having gone to such lengths, they would use the magic productively rather than just letting it swirl about. This enormous mass of magic must be actively achieving some goal that could not be done at lesser cost, or perhaps it is reactive or defensive in nature...
Is what Tanya would think, if she were in her old world. And then she'd give this forest a very wide berth, because the people behind this massive spell would surely have a lot of magical firepower reserved for unwelcome intruders.