Is "boi się jak ognia" idiomatic phrase?
I looked up online dictionaries saying "ognia" means "fire." However as far as following sentence goes, it pretty much doesn't make sense.

Tadzik (Mateusz Kościukiewicz) został wyekspediowany do ciotki, poza miasto, tak aby nie sprawiał problemów i nie wymagał opieki, której siostra boi się jak ognia.

So the question comes. In a sentence, it's translated like:

Tadzik (Matthew Kościukiewicz) was dispatched to my aunt, out of the city, so that did not cause any problems and did not require care, whose sister is afraid of it like the plague.

Any error in this translation, doesn't matter, I understand except the last word. It looks like "ognia" corresponds to "plague." Am I right?

Question

Is "boi się jak ognia" idiomatic phrase?
I looked up online dictionaries saying "ognia" means "fire." However as far as following sentence goes, it pretty much doesn't make sense.

Tadzik (Mateusz Kościukiewicz) został wyekspediowany do ciotki, poza miasto, tak aby nie sprawiał problemów i nie wymagał opieki, której siostra boi się jak ognia.

So the question comes. In a sentence, it's translated like:

Tadzik (Matthew Kościukiewicz) was dispatched to my aunt, out of the city, so that did not cause any problems and did not require care, whose sister is afraid of it like the plague.

Any error in this translation, doesn't matter, I understand except the last word. It looks like "ognia" corresponds to "plague." Am I right?

Answer

Merci pour vous.

Answer

Yes it's idiomatic. It means to be completely afraid of something, we assume that fire is the thing everybody fears. It's a very common phrase, in English it can be translated this way.
The sister is afraid of the responsibility over the brother, it corresponds to 'opieka'. 'Whose' isn't the most fortunate translation here.

Answer

Yes, "bać się czegoś jak ognia" means afraid of sth very much, like e.g. plague :)