Hm. Note that what Dina has is a scar on her arm - now pretty long, twisting and forking like lightning scar, dark purple in color that actually emits a faint glow when she draws on the dark power - but it's not a crystalline surface. It definitely doesn't seem to be the same case as with the dead wolves, who appeared to have had actual Taint crystals embedded in their bodies (but which are now only a dull purple color in appearance, and do not glow - perhaps because the beasts are dead?)
Though it's hard to tell just how old this Taint presence is, it has only relatively recently been manifesting openly. The party had an encounter with it just prior to Auri's and even Maggie's joining (one that you can assume was shared later with the others, to some detail at least), but that was an enclosed incident in Raziel's hidden temple up on Sandpeak Mountain. There, the corruption had destroyed a part of the temple and seemed to have remained dormant until the Chosen come across it (and Dina accidentally got infected). Elsewhere on the continent there were few isolated cases in the last few decades, mostly in the North, from which rumors might have originated describing some dark power connected to purple crystals. When Dina spoke to Arenov, the Archmage of Dunn's Mages Guild, even he was unable to tell her more except to mention these reports, and indeed stated that Dina herself seemed more knowledgeable on the subject.
As old as this thing potentially is, it's also kind of a new threat. And, for the time being at least, you've probably got the world's leading expert on it in your own party. I wish I could be more helpful! *woof*