I can easily come up with an explanation for a young, inexperienced adept of Blood or Death magic fumbling a ritual and therefore opening a rift to another dimension and getting pulled over the other side by a demon (66 on the Magic Mishaps table).
However, I can't easily understand the same happening to a young elvenspring druid girl that was trying to cast Healing Hands for the first time in a meadow, surrounded by fawns and white rabbits.
What's the explanation druid masters have for such events? Has druidic magic always been this dangerous or is this sort of stuff something that started happening in Ravenland since Zygofer's rise to power?
I don't think that's the kind of druids FbL is about... check out the introduction to Raven's Purge where Merigall shows the land to the former prisoner.
They are custodians of the order of nature, rational professionals who take care to maintain balance, not bothering to mess with fawns and rabbits unless they are a serious danger to that balance. And in that case most likely to cull their number, not to pet and cuddle them.
All magic carries with it the risk of attracting demonic presences and that's nothing new. Merigall, known demonic entity, travelled the land long before Zygofer tore open the Nexus. Admittedly it is probably more risky now since the veil was torn, but magic energies have always attracted demonic beings, no matter if they are druidic or sorcerous in nature. If you mess with arcane energies to manipulate the world you just have to face the consequences.